8.03 Addition and subtraction

Addition and subtraction (implied precision)

The number of decimal places in the result should be the same as the data with the least number of decimal places. e.g.
20.0cm +100.22cm
= 120.22cm
= 120.2cm (rounded down to one decimal place)

Note both numbers must be expressed in the same scale to apply this rule
e.g. 100.0m + 10.0cm
first convert both to metres i.e.
100.0m + 0.100m = 100.1m (rounded to 1.dp)

Addition and subtraction explicit precision

When adding or subtracting then simply add the uncertainties together.
e.g. (25 +/- 1mm) (10 +/- 2mm)
= 15 +/- 3mm)