I actually posted this on Yahoo answers, but I have no idea what they were saying... Let's say I used a micrometer to measure the dimensions of a cuboid. Length: 2.8850 cm (Uncertainty = 0.00005 cm) Width: 2.8750 cm (Uncertainty = 0.00005 cm) Height: 2.8950 cm (Uncertainty = 0.00005 cm) The volume is 24.01221563... cm3, and I have to round it off to 5 significant figures, hence the final answer is 24.012 cm3. Now I have to determine the possible error for the volume. There are two methods, i was told, one was to find the difference between the upper and lower limit. The other was to calculate the percentage error. So the percentage error for the length is: 0.00005/2.8850*100 = 0.0017331% % error for the width is: 0.00005/2.8750*100 = 0.0017391% % error for the height is: 0.00005/2.8950*100 = 0.0017271% Then I added them up. Total percentage error: 0.0051993% Multiply that by the volume and I get the possible error for the volume: 0.1248467127cm3 Now the question is, how should I round up this possible error? Should I round it off to 5 sig. fig. (same as the volume), or should I round it off to 4 decimal places? I'm wondering, because if I round it off to 5 sig. fig., I'll have a ridiculously accurate possible error.