Question

How do I round my answer for a measurement to appropriate significant figures if the measuring tool gives the measurements in increments of 2, 4, 6, etc.?

Do I round it to the nearest whole number or approximate it to the nearest tenth decimal place? I'm trying to figure out whether to say "It's closer to the two than where the three would be, I'll put two", or "It's almost but not quite on the two marking, I'll put 2.1 or 2.2?"

Answer 1

Yes, you should use one decimal place in this case.

Explanation:

Something worth knowing when performing measurements is that the last digit of the measurement value you record should always be a digit of uncertainty (never more than one digit can be uncertain!).

Thus, if the increments are posted with one significant figure like `2` `"mL"`, `4` `"mL"`, `6` `"mL"` etc. (or whatever unit it is, I'm assuming a graduated cylinder for example purposes. Measurement values should always have an associated unit), the measurement value you record should have one decimal place.

So yes, if the measurement is closer to `2` `"mL"` then `3` `"mL"`, you would write one decimal place acting as a "digit of uncertainty" to emphasize roughly where the measurement is, whether it be `2.3` `"mL"` or `2.2` `"mL"`, etc. However, never include more than one digit of uncertainty, i.e. do NOT record this measurement with two decimal places, such as `2.27` `"mL"`.