For a stable (i.e. non fluctuating) reading, the error estimated should be half that of the resolution.
EXAMPLE: If an autopipettor can be set between 1 and 5 ml with 0.05 ml increments (e.g. can be set at 1.00 ml, 1.05 ml, 1.10 ml, 1.15 ml, ...) -
- It is assumed that it will be accurate to its set-point resolution, i.e. if set at 1.10 ml it is assumed that the actual volume delivered will be closer to 1.10 ml than 1.05 or 1.15 ml.
- This means the volume delivered must be between (1.10+1.05)/2 and (1.10+1.15)/2 ml, i.e between 1.075 and 1.125.
- Therefore the volume delivered, V = 1.100 ± 0.025 ml.
Question 7
A Voltmeter is shown below.
The reading taken from this meter is 1.49 Volts. The error in this reading is -