metrology.sound_level_meter

Periodic tests of a sound level meter (IEC 61672-3:2013): the verdict.

IEC 61672-3:2013 is the short list of tests a laboratory runs on a working sound level meter every year or two, to show that it still meets the class it was built to under IEC 61672-1:2013. The laboratory measures; this module grades what it measured, clause by clause, and writes the statement Clause 22 prescribes for the outcome.

The rule. Every result is judged by the conformance rule of IEC TC 29 that 4.1 states (phonometry.metrology.verify_conformance): the measured deviation from the design goal within the acceptance limits and the laboratory’s actual expanded uncertainty, for a coverage probability of 95 %, within the maximum permitted by Table B.1 of IEC 61672-1, both limits inclusive. A result whose uncertainty exceeds its maximum “shall not be used to evaluate conformance” (4.3): it is neither a pass nor, by itself, a failure of the meter, SoundLevelMeterPeriodicVerification.unusable lists it and the verdict does not pass while it is there.

The manufacturer’s correction data (4.4). The acoustical test of the frequency weighting (Clause 12) and the electrical one (Clause 13, 13.7) correct the indications with the manufacturer’s free-field or random-incidence correction data, whose uncertainty the laboratory’s budget carries. The laboratory’s uncertainty without it “shall not exceed” the maximum; when the total exceeds the maximum only because of it, “testing may proceed”, and the result is one that did not conform, with the reason the NOTE to 22 t) gives in the statement. The record takes that uncertainty beside the total, SoundLevelMeterPeriodicMeasurements.acoustic_weighting_uncertainties_without_correction_data_db and its Clause 13 twin, and a result it clears is listed under SoundLevelMeterPeriodicVerification.over_maximum_by_correction_data and SoundLevelMeterPeriodicVerification.failed rather than under unusable. Without it the total is all the verdict knows, and 4.3 applies.

What is graded, with the acceptance limits of IEC 61672-1:2013 each clause of IEC 61672-3 points to and the maximum of its Table B.1:

• acoustic_weighting (12): the relative frequency weighting at 125 Hz and 8 kHz, relative to 1 kHz (12.7, 12.15), against Table 3, with 0,60 dB and 0,70 dB;
• electrical_weighting (13): every frequency weighting the meter provides at the octave frequencies of 13.4 (63 Hz to 16 kHz for class 1, to 8 kHz for class 2), against Table 3, with 0,60 dB up to 4 kHz, 0,70 dB above it and 1,00 dB above 10 kHz;
• weighting_at_1khz (14.2): C and Z against A at 1 kHz, 5.5.9, +/-0,2 dB, with 0,20 dB;
• time_weighting_at_1khz (14.3): S and time-averaged against F at 1 kHz, 5.8.3, +/-0,1 dB, with 0,20 dB (the maximum uncertainty is larger than the acceptance limit, as the page prints them);
• long_term_stability (15): the final minus the initial indication over 25 min to 35 min, 5.14.2, +/-0,1 dB (class 1) or +/-0,3 dB (class 2), with 0,10 dB;
• level_linearity (16): the level linearity deviations at 8 kHz on the reference level range, 5.6.5, +/-0,8 dB or +/-1,1 dB, with 0,30 dB; and the absence of an overload or under-range indication within the linear operating range the instruction manual states (16.4; IEC 61672-1 5.6.10);
• range_linearity (17): the level linearity deviations including the level range control, the same limits;
• toneburst (18): the 4 kHz toneburst responses of 18.5 to 18.7 less the reference responses of Table 4, against its limits, with 0,30 dB;
• c_peak (19): $L_{\mathrm{Cpeak}}-L_{\mathrm{C}}$ for one cycle at 8 kHz and the two half cycles at 500 Hz, less the reference differences of Table 5, against its limits, with 0,35 dB; and the absence of an overload indication while those signals are applied (19.3, 19.5);
• overload (20): the difference between the positive and the negative one-half-cycle input levels that first cause an overload indication, 5.11.3, 1,5 dB either way, with 0,25 dB; and the latching of the indicator (20.5);
• high_level_stability (21): the final minus the initial indication over 5 min near the top of the least-sensitive range, 5.15.2, +/-0,1 dB or +/-0,3 dB, with 0,10 dB.

What is recorded, not graded. The indications at the calibration check frequency before and after adjustment (Clause 10) and the self-generated noise (Clause 11), which “is reported for information only and is not used to assess conformance to a requirement” and without an uncertainty (11.1.2, NOTE 2). Both are still part of a complete test, so a record without them is incomplete. The environmental conditions (Clause 7) are checked against the ranges of 7.1, and a test outside them is not a valid periodic test: its statement says so before anything its results would say.

What a complete test covers. 8.1 asks for every test of a design feature IEC 61672-1 requires and the meter provides. A record shows a feature through the results it holds, and SoundLevelMeterFeatures declares the optional ones the meter has or lacks, as its instruction manual states them; the verdict holds the record to both: frequency weighting A always and C for class 1 (5.1.9, 5.1.10), C as well for a meter that measures C-weighted peak sound level, which “shall also be able to measure C-weighted time-averaged sound levels” (5.1.10), and every weighting declared or named by a clause of the record, tested in Clause 13, in the self-generated noise of 11.2 and, C and Z, in 14.2. The displays are held to the same rule both ways: the F, S and time-averaged displays are tested in the toneburst tests of Clause 18, where 18.2 calculates the sound exposure level from the time-averaged one for a meter that does not measure it, and a display another clause shows is compared with F in 14.3: S for a meter whose S-time-weighted toneburst response Clause 18 holds, time-averaged for a meter whose overload indication Clause 20 holds, as 20.1 tests only a meter that displays time-averaged sound level. Clause 20 in turn is required of a meter 14.3 shows to display time-averaged sound level, Clause 17 of a meter with more than one level range (17.1) and Clause 19 of one that measures C-weighted peak sound level. A measured clause is held to the extent its procedure gives: the steps of Clause 16 rise from the starting point in 5 dB steps until within 5 dB of the upper boundary of the linear operating range and in 1 dB steps from there up to the first overload indication, and fall the same way down to the first under-range indication (16.3), so the record carries that range, the starting point and the two indications; Clause 17 records 5 dB above the first indication of under-range on every level range, the reference one included (17.4), and the reference sound level held on every other one (17.3), whose number the declared features give. A declared feature carries what IEC 61672-1 makes of it: a meter without frequency weighting C measures no C-weighted peak sound level (5.1.10), one without the F time weighting has no S either (5.1.9), and one without F, a time-averaged display or sound exposure level indicates nothing 5.1.9 asks of a sound level meter and is refused. SoundLevelMeterPeriodicVerification.missing names the clauses a complete test lacks, SoundLevelMeterPeriodicVerification.incomplete what a measured clause is short of, SoundLevelMeterPeriodicVerification.not_applicable the clauses a feature declared absent takes out, and SoundLevelMeterPeriodicVerification.undeclared the features the record neither shows nor declares, which a record that left their tests out cannot be told from: the verdict does not pass while one is open.

The tables. The acceptance limits of Table 3 are read through phonometry.filters.weighting_class_limits, which already publishes them. Table 4 (the reference toneburst responses), Table 5 (the reference differences of the C-weighted peak) and Table B.1 (the maximum-permitted uncertainties) are published here, read-only, as IEC61672_TABLE_4, IEC61672_TABLE_5 and IEC61672_TABLE_B1.

What a pass here is, and is not. It is a verdict on the numbers put in: the preliminary inspection (Clause 5), the power supply (Clause 6), the calibrator’s own conformance to IEC 60942 (Clause 9, which phonometry.metrology.verify_sound_calibrator grades), the general test requirements of 8.2 to 8.5 (among them the confirmation of 8.4 that an electrical output used for the tests reads as the display does) and the source of the correction data (12.2 to 12.6) are the laboratory’s record. And even a meter that passes every periodic test supports no general conclusion about the specifications of IEC 61672-1 unless the model’s pattern approval under IEC 61672-2 is publicly available and the correction data for the acoustical test came from the instruction manual (Clause 1; 22 r and s): the statement the verdict writes is the one Clause 22 prescribes for the case at hand. Both are the laboratory’s to declare, as 22 c) and 12.5 have it state them, and the verdict assumes neither: without both declared it writes 22 s).

Oracle: BS EN 61672-3:2013 (IEC 61672-3:2013) and BS EN 61672-1:2013 (IEC 61672-1:2013), PDF page = printed folio + 2 in both. Tables 3 (folio 22), 4 (25), 5 (28) and B.1 (42 and 43) of Part 1; the clauses of Part 3 on folios 6 to 19.

Auto-generated from the source docstrings by scripts/generate_api_docs.py (make api-docs). Do not edit by hand.

Constant (tuple).

ACOUSTIC_TEST_FREQUENCIES_HZ = (125.0, 8000.0)

Constant (mapping).

ELECTRICAL_TEST_FREQUENCIES_HZ = {1: (63.0, 125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0, 8000.0, 16000.0), 2: (63.0, 125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0, 8000.0)}

Constant (mapping).

Constant (tuple).

IEC61672_TABLE_5 = (PeakReference(signal='one cycle', nominal_frequency_hz=31.5, reference_difference_db=2.5, class_1_limits_db=(-2.0, 2.0), class_2_limits_db=(-3.0, 3.0)), PeakReference(signal='one cycle', nominal_frequency_hz=500.0, reference_difference_db=3.5, class_1_limits_db=(-1.0, 1.0), class_2_limits_db=(-2.0, 2.0)), PeakReference(signal='one cycle', nominal_frequency_hz=8000.0, reference_difference_db=3.4, class_1_limits_db=(-2.0, 2.0), class_2_limits_db=(-3.0, 3.0)), PeakReference(signal='positive half cycle', nominal_frequency_hz=500.0, reference_difference_db=2.4, class_1_limits_db=(-1.0, 1.0), class_2_limits_db=(-2.0, 2.0)), PeakReference(signal='negative half cycle', nominal_frequency_hz=500.0, reference_difference_db=2.4, class_1_limits_db=(-1.0, 1.0), class_2_limits_db=(-2.0, 2.0)))

Constant (tuple).

MaxUncertaintyRow(
    requirement: str,
    reference: str,
    max_uncertainty: float,
    unit: str = 'dB',
    lower_hz: float | None = None,
    upper_hz: float | None = None,
    includes_lower: bool = True,
)

One row of IEC 61672-1:2013 Table B.1, a maximum-permitted uncertainty.

Attributes

MaxUncertaintyRow.contains(frequency_hz: float) -> bool

Whether a nominal frequency falls in the row’s band.

A row that is not banded by frequency contains every frequency.

Parameters

Returns: True inside the band, its included ends counted.

PeakReference(
    signal: str,
    nominal_frequency_hz: float,
    reference_difference_db: float,
    class_1_limits_db: tuple[float, float],
    class_2_limits_db: tuple[float, float],
)

One row of IEC 61672-1:2013 Table 5, the C-weighted peak reference difference.

Attributes

PeakReference.limits_db(meter_class: int) -> tuple[float, float]

The (lower, upper) acceptance limits for a class, in decibels.

Parameters

Returns: The limits of that class’s column.

Raises

Constant (mapping).

PERIODIC_TEST_ENVIRONMENT = {'static_pressures_kpa': (80.0, 105.0), 'air_temperatures_c': (20.0, 26.0), 'relative_humidities_percent': (25.0, 70.0)}

Constant (tuple).

SLM_PERIODIC_REQUIREMENTS = ('acoustic_weighting', 'electrical_weighting', 'weighting_at_1khz', 'time_weighting_at_1khz', 'long_term_stability', 'level_linearity', 'range_linearity', 'toneburst', 'c_peak', 'overload', 'high_level_stability')

SoundLevelMeterFeatures(
    *,
    c_weighting: bool | None = None,
    z_weighting: bool | None = None,
    f_time_weighting: bool | None = None,
    s_time_weighting: bool | None = None,
    time_averaged: bool | None = None,
    sound_exposure_level: bool | None = None,
    level_ranges: int | None = None,
    c_weighted_peak: bool | None = None,
)

Which optional design features of IEC 61672-1:2013 a sound level meter has.

IEC 61672-3:2013 8.1: the periodic tests “apply only for those design features that are required by IEC 61672-1 and that are available in the sound level meter submitted for test. All such features shall be tested.” A record shows that a meter has a feature by holding its results; it cannot show that the meter lacks one, and a meter with one level range reads the same as a record that left Clause 17 out. The instruction manual says which features the meter has (IEC 61672-1 5.1.9, 5.1.10, 5.1.12), and each field carries that answer: True the meter has the feature, False it has not, None (the default) not declared, and for the level ranges their number. The verdict owes the tests of every feature declared or shown, lists the clauses a feature declared absent takes out of the test under SoundLevelMeterPeriodicVerification.not_applicable, and holds a feature neither declared nor shown as an open question that keeps the test incomplete, under SoundLevelMeterPeriodicVerification.undeclared, as it holds the number of level ranges of a meter Clause 17 shows to have several, which 17.3 and 17.4 cover. A feature declared absent takes with it the one IEC 61672-1 makes depend on it: without frequency weighting C the meter measures no C-weighted peak sound level (5.1.10), and without the F time weighting it has no S (5.1.9). Frequency weighting A has no field: every meter has it (5.1.9).

Attributes

SoundLevelMeterPeriodicMeasurements(
    *,
    static_pressures_kpa: Sequence[float] | None = None,
    air_temperatures_c: Sequence[float] | None = None,
    relative_humidities_percent: Sequence[float] | None = None,
    calibration_check_initial_db: float | None = None,
    calibration_check_adjusted_db: float | None = None,
    self_noise_microphone_db: float | None = None,
    self_noise_electrical_db: Mapping[str, float] | None = None,
    acoustic_weighting_deviations_db: Sequence[float] | None = None,
    acoustic_weighting_uncertainties_db: Sequence[float] | None = None,
    acoustic_weighting_uncertainties_without_correction_data_db: Sequence[float] | None = None,
    electrical_weighting_deviations_db: Mapping[str, Sequence[float]] | None = None,
    electrical_weighting_uncertainties_db: Mapping[str, Sequence[float]] | None = None,
    electrical_weighting_uncertainties_without_correction_data_db: Mapping[str, Sequence[float]] | None = None,
    weighting_at_1khz_deviations_db: Mapping[str, float] | None = None,
    weighting_at_1khz_uncertainties_db: Mapping[str, float] | None = None,
    time_weighting_at_1khz_deviations_db: Mapping[str, float] | None = None,
    time_weighting_at_1khz_uncertainties_db: Mapping[str, float] | None = None,
    long_term_stability_db: float | None = None,
    long_term_stability_uncertainty_db: float | None = None,
    linearity_deviations_db: Sequence[float] | None = None,
    linearity_uncertainties_db: Sequence[float] | None = None,
    linearity_levels_db: Sequence[float] | None = None,
    linear_operating_range_db: Sequence[float] | None = None,
    linearity_starting_point_db: float | None = None,
    linearity_overload_level_db: float | None = None,
    linearity_under_range_level_db: float | None = None,
    range_linearity_deviations_db: Mapping[str, Sequence[float]] | None = None,
    range_linearity_uncertainties_db: Mapping[str, Sequence[float]] | None = None,
    toneburst_responses_db: Mapping[str, Sequence[float]] | None = None,
    toneburst_uncertainties_db: Mapping[str, Sequence[float]] | None = None,
    c_peak_differences_db: Sequence[float] | None = None,
    c_peak_uncertainties_db: Sequence[float] | None = None,
    c_peak_overload_indicated: bool | None = None,
    overload_difference_db: float | None = None,
    overload_uncertainty_db: float | None = None,
    overload_latched: bool | None = None,
    high_level_stability_db: float | None = None,
    high_level_stability_uncertainty_db: float | None = None,
)

What a laboratory measured in the periodic tests of IEC 61672-3:2013.

Every graded result comes with the actual expanded uncertainty the laboratory calculated for it, for a coverage probability of 95 % (4.2), in the same position or under the same key. A clause left at None was not measured. Levels and deviations are in decibels, and every field is keyword-only, so the unit in its name is written at the call site.

Attributes

SoundLevelMeterPeriodicRequirement(
    name: str,
    clause: str,
    tables: str,
    labels: tuple[str, ...],
    verifications: tuple[ConformanceVerification, ...],
    checks: tuple[tuple[str, bool], ...] = (),
    over_maximum_by_correction_data: tuple[str, ...] = (),
)

The verdict on one requirement of IEC 61672-3:2013.

Attributes

property

The results that did not conform, and the failed checks.

A result outside its acceptance limits and measured with an acceptable uncertainty, or one of over_maximum_by_correction_data (4.4). A result that is unusable shows nothing about the meter (4.3) and is not here.

SoundLevelMeterPeriodicRequirement.failure_reason(label: str) -> str

Why a result or a check did not complete, as 22 t) states it.

Parameters

Returns: The reason, in the words of the NOTE to 22 t) where it prints them.

Raises

property

Whether every result conforms (4.1) and every check held.

SoundLevelMeterPeriodicRequirement.plot(
    ax: Axes | None = None,
    *,
    language: str = 'en',
    **kwargs: Any,
) -> Axes

Draw every result of the requirement against its limits.

As IEC 61672-1:2013 Figure C.1 draws its examples: the acceptance limits, the deviation from the design goal, the actual uncertainty as its error bar and the maximum permitted as the band behind it. The electrical test of the frequency weightings, whose limits run from 0,7 dB to 16 dB, is drawn as each result’s margin to its nearer limit instead. A result whose uncertainty exceeds its maximum is drawn hollow, as 4.3 forbids using it, and a result of over_maximum_by_correction_data as one that did not conform (4.4). The title names the clause and its verdict above the clause’s heading.

Requires matplotlib (pip install phonometry[plot]); returns the Axes.

Parameters

property

What the clause tests, as its heading reads.

property

The results whose uncertainty exceeds the maximum permitted (4.3).

All of them but those of over_maximum_by_correction_data, which 4.4 lets the test proceed with.

SoundLevelMeterPeriodicVerification(
    meter_class: int,
    pattern_approval_public: bool,
    corrections_in_manual: bool,
    measurements: SoundLevelMeterPeriodicMeasurements,
    requirements: tuple[SoundLevelMeterPeriodicRequirement, ...],
    features: SoundLevelMeterFeatures = ...,
)

The IEC 61672-3:2013 verdict on the periodic tests of a sound level meter.

Attributes

property

The environmental readings outside the ranges of 7.1.

Periodic tests “shall be performed within” 80 kPa to 105 kPa, 20 °C to 26 °C and 25 % to 70 % (7.1); a test outside them is not a valid periodic test, whatever its results.

property

(clause, result) for every result that did not conform or check failed.

A result outside its limits with an acceptable uncertainty, a result over its maximum only by the manufacturer’s correction data (4.4), and a failed yes/no check.

property

(clause, what is short) for every measured clause short of a result.

A clause not measured at all is in missing instead; see the module docstring for what 8.1 makes a complete test.

property

The clauses a complete periodic test holds that the record lacks.

Clauses 7, 10, 11, 12, 13, 15, 16, 18 and 21 for every meter; 14.2 for a meter with C or Z, which class 1 always has (IEC 61672-1 5.1.10) and any clause of a class 2 record can show, a C-weighted peak result included (5.1.10); 14.3 for a meter with F that another clause shows to display S (an S toneburst of Clause 18) or time-averaged sound level (the overload test of Clause 20, 20.1); Clause 20 for a meter 14.3 shows to display time-averaged sound level ("eq"), which 20.1 tests; and each of them, Clause 17 and Clause 19 as well, for a meter whose features declare what the clause tests. A record cannot show that a meter lacks a feature: a feature neither declared nor shown is under undeclared, and a clause a feature declared absent takes out is under not_applicable.

property

(clause, why) for every clause the declared features take out.

8.1 applies the periodic tests only to the features the meter has: 14.2 to a meter with C or Z besides A, 14.3 to one with F and S or a time-averaged display, Clause 17 to one with more than one level range (17.1), Clause 19 to one that measures C-weighted peak sound level and Clause 20 to one that displays time-averaged sound level (20.1). A clause is here when features declare the meter without what it tests, or without the feature it needs: Clause 19 for a meter declared without frequency weighting C (IEC 61672-1 5.1.10). It is neither missing nor needed for a pass.

property

(clause, result) for every result over its maximum only by 4.4.

Its uncertainty exceeds the maximum only because it includes the uncertainty of the manufacturer’s correction data: the test proceeds, and the result is one that did not conform (4.4), for the reason the NOTE to 22 t) gives. Each is in failed as well.

property

Whether the meter completed the periodic tests successfully.

Every clause a complete test holds was measured on everything it requires (nothing missing or incomplete), every optional feature is declared or shown (nothing undeclared), the tests were within the environmental conditions of 7.1, and every result conforms: no deviation outside its limits, no uncertainty above its maximum and no failed check.

SoundLevelMeterPeriodicVerification.plot(
    ax: Axes | None = None,
    *,
    language: str = 'en',
    **kwargs: Any,
) -> Axes

Draw every graded clause at its margin to its acceptance limits.

One slot per clause, however many results it holds: each result’s distance from its deviation to the nearer acceptance limit is a dash, and the result that decides the clause is marked over them with its actual uncertainty as error bar; a result at or above zero lies within its limits. The mark is a cross for a result that did not conform, one over its maximum only by the manufacturer’s correction data included (4.4), hollow for one 4.3 forbids using, and otherwise a diamond at the result nearest its limit. Each requirement’s own SoundLevelMeterPeriodicRequirement.plot draws its results one by one.

Requires matplotlib (pip install phonometry[plot]); returns the Axes.

Parameters

SoundLevelMeterPeriodicVerification.requirement(
    name: str,
) -> SoundLevelMeterPeriodicRequirement

The verdict on one requirement.

Parameters

Returns: Its SoundLevelMeterPeriodicRequirement.

Raises

property

The statement IEC 61672-3:2013 Clause 22 prescribes for the result.

In this order, the first that applies: a notice when the tests were not performed within the conditions of 7.1, as tests outside them are not periodic tests to IEC 61672-3, whatever their results, and none of 22 r), s) and t) is theirs; 22 t) when a result exceeds its limits, a check fails or a result exceeds its maximum only by the uncertainty of the manufacturer’s correction data (4.4), followed by the tests not completed and why, as a result that did not conform settles the verdict whatever the others are; the 4.3 notice when results cannot be used; a notice naming the clauses not measured, what a clause lacks and the features not declared, as 22 r) and s) both need the results of all the periodic tests; and otherwise 22 r) with a public pattern approval and correction data from the manual, or 22 s) without either, which carries the caveat of Clause 1.

property

(feature, what is open) for every feature neither declared nor shown.

A feature the record shows through a result is the meter’s; one the record holds no result of may be absent from the meter or left out of the test, and only features can tell the two apart (8.1). Each such feature, a field of SoundLevelMeterFeatures, keeps the test from passing until it is declared. The sound exposure level is not asked for when the meter displays time-averaged sound level, from which 18.2 calculates it anyway. The number of level ranges stays open for a meter Clause 17 shows to have several until it is declared, as 17.4 covers every level range and 17.3 every one besides the reference level range.

property

(clause, result) for every result 4.3 forbids using.

Constant (mapping).

TONEBURST_TEST_DURATIONS_MS = {'F': (200.0, 2.0, 0.25), 'S': (200.0, 2.0), 'E': (200.0, 2.0, 0.25)}

ToneburstReference(
    duration_ms: float,
    reference_response_db: float,
    class_1_limits_db: tuple[float, float],
    class_2_limits_db: tuple[float, float],
)

One row of IEC 61672-1:2013 Table 4, the reference 4 kHz toneburst response.

Attributes

ToneburstReference.limits_db(meter_class: int) -> tuple[float, float]

The (lower, upper) acceptance limits for a class, in decibels.

Parameters

Returns: The limits of that class’s column.

Raises

verify_sound_level_meter_periodic(
    meter_class: int,
    measurements: SoundLevelMeterPeriodicMeasurements,
    *,
    pattern_approval_public: bool = False,
    corrections_in_manual: bool = False,
    features: SoundLevelMeterFeatures | None = None,
) -> SoundLevelMeterPeriodicVerification

Grade the periodic tests of a sound level meter, IEC 61672-3:2013.

Each requirement measured is judged result by result by the conformance rule of IEC TC 29 (4.1), with the acceptance limits IEC 61672-1:2013 prints for it and the maximum-permitted uncertainties of its Table B.1; see the module docstring for which clause reads which. The verdict passes when the record is complete, the tests were performed within the conditions of 7.1 and every result conforms; its statement is the text Clause 22 prescribes for the case. A frequency-weighting result whose uncertainty exceeds its maximum only because of the manufacturer’s correction data is a result that did not conform, by 4.4, when the record gives the uncertainty without that data. The optional features of the meter (8.1) are what features declares and what the record shows; a feature neither declared nor shown keeps the verdict from passing, as a record that left a test out reads the same as a meter without the feature.

Parameters

Returns: A SoundLevelMeterPeriodicVerification.

Raises