What is the lowest mass measurable using a 4 decimal point analytical balance?
Keep in mind that for many analytical instruments, you cannot assume that the uncertainty is ± the last digit.
It's usually necessary to look at the specifications in the manual or on a sticker to find the measured uncertainty.
For instance, one of our balances, a Sartorius CPA225D (manual), is readable to 0.01 mg (i.e. the display can display increments of 0.01 mg), but the specifications list the repeatability as only ±0.05 mg (±1 s.d.).
This means that repeated measurements of the same mass will be (ideally) normally distributed with a standard deviation of 0.05 mg and that even though the instrument has the resolution to report in 0.01 mg increments, the uncertainty in a measurement is higher.