Field Inspection manual — Inspection Preparation
Table of Contents
 Inspection Preparation
 Entrance Interview
 Exit Interview
 Appendix I — Conversion Factors Table
 Appendix II — Linear Interpolation
 Appendix III — Break Point Determination
Inspection Preparation
Prior to initiating any inspection, the inspector should check the establishment records to determine:
 the number and type of devices located in the establishment;
 any specialized equipment or test product requirements;
 previous enforcement action(s) and/or restrictions.
Entrance Interview
During the course of the entrance interview, the inspector shall:
 identify themselves to the person in charge of the inspection site by showing their identification card and presenting a business card;
 state the purpose of the inspection visit, briefly explain what the inspection will entail and advise of any special requirements ^{Footnote 1} (i.e. equipment, product, slowing or stopping work in a particular area) ^{Footnote 2}; and
 identify and adhere to all establishment and departmental safety rules ^{Footnote 3}.
Exit Interview
During the course of the exit interview, the inspector shall ensure that the trader understands:
 the results of the inspection (even if no violations were encountered); and
 any followup action which must be taken to correct non compliances ^{Footnote 4}.
The inspector shall provide the trader with a copy of all inspection documentation. The inspector shall ask the trader to sign the inspection report and all associated documentation ^{Footnote 5}.
Appendix I — Conversion Factors
To convert from  to  multiply by 

yards  metre  0.914 4 
gallons  cubic metres  0.004 546 09 
pounds  kilograms  0.453 592 37 
feet  metres  0.304 8 
feet  millimetres  304.8 
inches  millimetres  25.40 
square yards  square metres  0.836 127 36 
square feet  square metres  0.092 903 04 
square inches  square centimetres  6.451 6 
square inches  square millimetres  645.16 
cubic yards  cubic metres  0.764 554 8 
cubic feet  cubic metres  0.028 316 8 
cubic inches  cubic centimetres  16.387 064 
gallons  litres  4.546 09 
quarts  litres  1.136 52 
pints  litres  0.568 261 
pints  millilitres or cubic centimetres  568.261 
½ pints  litres  0.284 131 
½ pints  millilitres or cubic centimetres  284.130 742 
fluid ounces  millilitres or cubic centimetres  28.413 
ounces (avoirdupois)  grams  28.349 5 
tons (short)  kilograms  907.184 74 
tons (short)  metric tons  0.907 184 74 
Note: Some factors may have been rounded off.
To convert from  to  multiply by 

metres  yards  1.093 6 
cubic metres  gallons  219.969 
kilograms  pounds  2.204 623 
metres  feet  3.280 81 
millimetres  feet  0.003 281 
millimetres  inches  0.039 37 
square metres  square yards  1.196 
square metres  square feet  10.764 
square centimetres  square inches  0.155 
square millimetres  square inches  0.001 55 
cubic metres  cubic yards  1.307 951 
cubic metres  cubic feet  35.314 667 
cubic centimetres  cubic inches  0.061 024 
litres  gallons  0.219 969 
litres  quarts  0.879 877 
litres  pints  1.759 753 
millilitres or cubic centimetres  pints  0.001 76 
litres  ½ pints  3.519 5 
millilitres or cubic centimetres  ½ pints  0.003 519 
millilitres or cubic centimetres  fluid ounces  0.035 195 
grams  ounces  0.035 274 
kilograms  tons (short)  0.001 102 3 
metric tonnes  tons (short)  1.102 3 
Note: Some factors may have been rounded off.
Appendix II — Linear Interpolation
There are occasions when an inspector may need to interpolate values between two known values. This is common when assessing percentage tolerances, or applying various correction factors to a measured quantity. While not difficult to calculate, it is important that the interpolated value be determined carefully and correctly.
The formula for linear interpolation is:
Where:
 A_{upper} = Upper Known Value
 A_{lower} = Lower Known Value
 B_{upper} = Upper Corresponding Value
 B_{lower} = Lower Corresponding Value
 A_{mid} = Mid Known Value
 B_{mid} = Mid Unknown Corresponding Value
The concept may be best described by example:
Example
Assume you are taking a temperature measurement with a certified thermometer. The thermometer is accompanied with a calibration certificate which lists "Indicated" and "True" temperatures. The temperature that you observe (26.50 °C) falls between two adjacent indicated values (20.00 °C & 30.00 °C) on the calibration certificate. How do you find the corresponding "True" temperature?
Indicated Temp  True temperature 

20.00 °C (A_{lower})  20.20 °C (B_{lower}) 
26.50 °C (A_{mid})  B_{mid} 
30.00 °C (A_{upper})  30.25 °C (B_{upper}) 
What is the true temperature for an indicated temperature of 26.5 °C?
 B_{mid} = [(30.25 − 20.20) (26.50 − 20.0)] ÷ (30.00 − 20.00) + 20.20
 B_{mid} = [(10.05)(6.50) ÷ 10.00] + 20.20
 B_{mid} = [65.325 ÷ 10.00] + 20.20
 B_{mid} = [6.5325] + 20.20
 B_{mid} = 26.7325
 B_{mid} ≈ 26.73 °C
This formula is useful for setting up a spreadsheet or a small program in a laptop, programmable calculator or PDA. If the interpolation must be calculated manually, the following simplified explanation may make it clearer.
Using a simplified approach:
Figure 1
Linear Extrapolation
Either of these two approaches may also be used for linear extrapolation (finding a value not contained within, but rather larger or smaller than the data set), although extreme care must be taken to ensure that the extrapolated value is in fact representative and valid. Extrapolation should not be used for calibration values unless authorized by the Regional Gravimetric Specialist.
Revision
Original Document
Appendix III — Break Point Determination
There are occasions when an inspector may need to determine the weight value to a finer resolution than the division of the scale will allow. This is a common occurrence for NonAutomatic weighing devices where tolerances may be expressed in terms of partial divisions. It is also used in development of test loads for both Automatic and NonAutomatic Weighing Devices. While not difficult to determine, it is important that this finer resolution be determined carefully and correctly. If a device is equipped with expanded resolution indications, this feature may be used instead of the following procedures.
Break Point (BP) is considered to be the edge of the Zone of Uncertainty within a division. The Zone of Uncertainty (ZU) is the point where the electronic indicator is no longer sure which graduation should be displayed. At this point, earlier devices will often flash between two adjacent indications. Newer devices may be equipped with features which will prevent the flashing of indications even though the Zone of Uncertainty has been reached. These devices will then require an additional load change equal to 0.1d or 0.2d before they will display the next indication. See Zone of Uncertainty Determination for more information.
It can be assumed that the width of the Zone of Uncertainty is ≤0.3d, if the device passes the Load Discrimination tests described in NAWDS STP14.
Break point determination shall be done with error weights of at least 0.1d. As environmental conditions can make it very difficult to properly determine Break Points, the inspector may be forced to use larger weights (0.25d − 0.3d), or forego break point testing altogether. It is important that it is actually the Break Point of the device being tested and not other external influences acting on the device which cause the indication to change.
It should be noted that Break Point determination at zero load may be affected by Automatic Zero Setting (AZSM) circuitry. Break Point determination should not be attempted at zero load on devices equipped with AZSM.
Devices equipped with Center of Zero (±0.25d) indicators may be assumed to be at the center of zero when the indicator is on. In these cases no further Break Point determination is required at zero load.
If a test load is being developed using a device which does not return to zero (i.e. by load differential), then Break Points should be established at both the upper and lower indicated values.
The following examples illustrate how to determine break points. The examples assume addition of error weights although the procedures are also valid in reverse  that is with removal of error weights.
The formula for break point determination is:
Where:
 W_{actual} = Actual Weight on Scale
 W_{ind} = Scale Indication
Example:
A vehicle scale with 10 kg divisions indicates 20 010 kg with a load. Using error weights (0.1 d), the inspectors adds 3 kg to make the indicator flash to 20 020 kg. The actual weight of the load on the scale is then calculated as:
 W_{actual} = (W_{ind} + ½ division) − error weights added
 W_{actual} = (20 010 kg + 5 kg) − 3 kg
 W_{actual} = 20 012 kg
The formula for developing a test load by load differential, when the scale does not return to zero, is:
Where:
 W_{test} = Actual Weight of Test Load
 W_{cap} = Loaded Scale Indication
 W_{low} = Unloaded Scale Indication
 E_{low} = Error Weights added to Unloaded Scale to reach Break Point
 E_{cap} = Error Weights added to Loaded Scale to reach Break Point
Example:
A 10 000 kg × 1 kg hopper scale is used to develop a test load at capacity. Due to product containment, the unloaded scale returns to 500 kg indicated. Using sample figures for the break points, the weight of this (partial) test load is determined as:
 W_{test} = (W_{cap} − W_{low}) + (E_{low} − E_{cap})
 W_{test} = (10 000 kg − 500 kg) + (0.4 kg − 0.2 kg)
 W_{test} = 9 500 kg + 0.2 kg
 W_{test} = 9 500.2 kg
Alternately, the scale could be preloaded at the lower indication (unloaded condition) with a sufficient quantity of test standards to place it in the center of an indicated value. Then, only the loaded break point would need to be found.
Figure 2
Zone of Uncertainty Determination
The width of the Zone of Uncertainty may be determined, if necessary. First, find the Lower Break Point. This is the point where the scale flashes between the lower and next higher divisions. Continue to add Error Weights (0.1d) until the display indicates solidly, the next higher division. This is the Upper Break Point. Determine the amount of Error Weights added between the Lower Break Point and the Upper Break Point. This is the width of the Zone of Uncertainty.
For devices which suppress the flashing display as mentioned previously, you must use an alternate procedure. Starting at the lower indication, add Error Weights until the next higher indication is displayed. Note how many error weights were added. Now remove Error Weights until the previous lower division is again indicated. You will note that the Break Points appear to move from a high to a low position. The amount of apparent movement evident is equal to the width of the Zone of Uncertainty.
Revision
Original Document
Footnotes
 Footnote 1

The inspector has the right to request and receive assistance from the trader or his/her staff, if necessary. The inspector will advise the trader of this requirement at the beginning of the inspection.
 Footnote 2

The inspector will minimize to the extent possible without jeopardizing the completeness of validity of the inspection, disruptions to the trader's business.
 Footnote 3

Occasionally an inspector may be asked to sign a paper agreeing to company safety rules and these will sometimes contain a waiver of company responsibility. The first is acceptable, but the inspector must not sign a waiver of responsibility.
 Footnote 4

When seizure or detention action is taken it must be clearly explained to the trader that moving or altering the device is prohibited unless written authority is granted by an inspector; and if such authority is granted, its scope and limitations should be clearly explained and supported by written direction or clearances.
 Footnote 5

If the trader refuses to sign the inspection documents, the inspector should not make an issue of it, but simply note this fact on the inspection report and bring the matter to the attention of the inspector's supervisor at the earliest opportunity.
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