mathers wrote:you are reading a USA manual if you see MPH and is not applicable to canada

The unit is the unit. It will not be more or less accurate whether you are north or south of the border. 1 mph = 1.6 kmh. The accuracy is the accuracy, whatever it may be.

The accuracy is based on the unit of measure used and does not matter what type of unit is being used, it is the same math for each unit.

(ie: 7apples divided by 3apples = 2.33apples / 7 kph divide by 3kph = 2.33. kph / 7L divide by 3L = 2.33L / 7inches divide by 3inches = 2.33inches)

+/- 1 is that the unit can almost always will never obtain a reading of say 100.000000 etc km/hr

but the reading could be 100.9999999 etc (which is up to the +1) however the unit always will round down to the nearest whole number being "100", (which is the minus 1), thus the rounding down on every reading is a benefit to the driver

mathers wrote:
If the advertised accuracy of the unit is +/- 1 mph (or 1 kmh, for that matter), this is irrelevant to the argument. Yours is a discussion of rounding, not accuracy. If the reading is 100.1, it rounds down to 100, but due to the accuracy being +/- 1kmh, the actual speed could be 99.1 (or 98.5, if +/- 1.6).

I know the difference between accuracy and rounding and that is specifically taught on course and why it the unit is accurate WITHIN + / - 1kph on each displayed reading. Because it is next to impossible to ever have a reading bang on the exact precise number after the calculation with decimal places. So that is where the accuracy part comes in...the true/precise accurate speed could be the 100.1kph as you describe, however the unit does not display in 10ths, 100ths or 1000ths etc, so it automatically programmed to round down to the nearest whole number, which would be 100. So in this case the unit is accurate within 0.1kph.
Above is merely a suggestion/thought and in no way constitutes legal advice or views of my employer. www.OHTA.ca