Round an answer to significant figures
Show a result with the right number of significant figures, and see how to count them.
Significant figures tell how precisely a number is known. A lab answer should not be more precise than the least precise measurement that went into it.
The simplest way to round to n significant figures is scientific display with n − 1 decimal places. For 3 significant figures, use 2 decimals: 4567.89 becomes 4.57 × 10³.
Counting rules in short: non-zero digits always count, zeros between digits count, leading zeros never count, and trailing zeros after a decimal point count.
- Open the Chemistry toolkit from the Reference library (Subject toolkits) and choose the Significant figures tab.
- Type a measurement such as 0.00450. The digits that count are highlighted and the toolkit tells you the total.
- To combine measurements, type an expression such as 12.11 + 18.0 + 1.013. The toolkit applies the addition or multiplication rule and shows which number limited the answer.
Classic Graphing 84
Start on the main screen: Press 2nd then mode (QUIT) to get back to the home screen. Pressing clear on a menu also backs out of it.
Press mode. Move right once to SCI and press enter. Then go down to the digits row, move right three times to 2, and press enter.
mode▶enter▼▶▶▶enterGo back to the home screen (2nd, mode), type 4567.89 and press enter.
2ndQUITmode4567.89enter
You should see4.57E3
Set the digits row back to FLOAT when you are done, or later answers will keep being rounded.
Natural Scientific 991
Start on the main screen: Press MENU, then 1 (Calculate) to return to the main calculation screen. AC clears the line you are on.
Press SHIFT then MENU (SETUP), choose Number Format (3), then Sci (2), and type 3 for 3 significant figures.
SHIFTSETUPMENU323Type 4567.89 and press = . The answer is a fraction at first; press S⇔D to see the decimal form.
4567.89=S⇔D
You should see4.57×10^3
Choose Norm in the same menu to go back to normal display.
RPN Scientific 15
Start on the main screen: There is no menu to leave. Press the back arrow to clear a number you are typing, or CLx (g then back arrow) to clear the X register.
Choose scientific display with f and SCI (the 8 key), then 2 for two digits after the point.
fSCI82Key in 4567.89. Once typed, the number is shown as 4.57 with the power 03.
4567.89
You should see4.57 03
Tips
- Round only at the end. Keep extra digits in the middle of a calculation, then round the final answer.
- The count for 4500 is unclear: the trailing zeros may or may not be measured. Write it as 4.50 × 10³ to show three figures.