MILPRF55110G
APPENDIX C
C.5.6
C.5.6 Resolution of measurement devices and test equipment. Unless otherwise specified (see 3.1.1), the
resolution of measurement devices and test equipment used for the evaluation of printed board performance shall be
at least a factor of 10 better than the limits or tolerances of a value to be determined. (For example: a voltmeter
resolution of +/ 0.1 percent to determine level to a tolerance of +/ 1 percent).
C.5.7
C.5.7 Values (true and nominal). The limits of size specified in this specification are for true values. Nominal
values are indicated by the inclusion of a tolerance. Proper allowance shall be made for measurement errors
(including those due to deviations from nominal test conditions) in establishing the working limits to be used for the
values to be measured, so that the values of the test specimen parameters (as they would be under nominal test
conditions) can be determined properly.
C.5.8
C.5.8 Numeric reporting. The results of printed wiring board verification shall be presented in accordance with test
method number 1.6 of IPC-TM-650.
C.5.9
C.5.9 Rounding of measurements. Values determined by measurement can be rounded to one decimal place
beyond the resolution specified. Example, the minimum etchback requirement is .0002 inch. The resolution required
of the measurement device in accordance with C.5.6 would to the +/ .00001 inch. In a case where an inspection/test
personnel uses an instrument capable of resolution to +/ .000001 inch, a measurement of .000186 inch is
determined for etchback on that test specimen. This value cannot be rounded to .0002 inch or even .00019 inch. It
can be truncated to .00018 inch or reported as taken as .000186 inch.
C.6
C.6. DEFINITIONS FOR TEST EQUIPMENT AND INSPECTION FACILITIES
C.6.1
C.6.1 Accuracy. A measure of the closeness of an individual measurement or the average of a number of
measurements to the true value. Accuracy includes a combination of random error (precision) and systematic error
(bias) components that are due to sampling and analytical operations.
C.6.2
C.6.2 Bias. The systematic or persistent distortion of a measurement process, which causes errors in one
direction (i.e., the expected sample measurement is different from the sample's true value).
C.6.3
C.6.3 Calibration. Calibration is an activity related to measurement and test equipment. Calibration is the
comparison of measurement standard, instrument, or item of known precision and bias with another standard,
instrument, or item to detect, correlate, report, or eliminate by adjustment, any variation in the precision and bias of
the item being compared. Use of calibrated measurement standard, instrument, or items provide the basis for value
traceability of product technical specifications to national standard values.
C.6.4
C.6.4 Measurement and testing equipment. Tools, gauges, instruments, sampling devices, or systems used to
calibrate, measure, test, or inspect in order to control or acquire data to verify conformance to specified requirements.
C.6.5
C.6.5 Precision. The degree to which a measurement standard, instrument, item, test, or process exhibits
repeatability. Expressed statistically or through various techniques of Statistical Process Control (SPC), the term is
many times used interchangeably with "repeatability". Precision is a measurement of how closely the analytical
results can be duplicated.
C.6.6
C.6.6 Resolution. The smallest unit of readability or indication of known value on an instrument, device, or
assemblage thereof. It is also related to the gradations on measuring instruments and the ability of the inspection/test
personnel to interpret between those gradations. The resolution value is frequently used in the device literature to
classify the instrument.
C.6.7
C 6.7 Tolerance (IPC-T-50). The total amount by which a specific dimension is permitted to vary. A tolerance is
indicated in this specification only if it is expressed as the variation about a specified value (also known as a "nominal
value").
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