Read each tool the way a scientist does: certain digits plus one estimated digit.
How to use
Pick a tool. Choose the Worksheet Set (3 fixed items) or Random practice.
Look at the lines. Write every digit you are sure of, then add one estimated digit.
Tap Check. If you miss, you get one retry. Then tap Show my results and copy it onto your worksheet.
Item 1 of 3Correct: 0 of 0
Why only one estimated digit?
The block ends between the 4.3 line and the 4.4 line. You can see 4.3, so those digits are certain.
Imagine the space between the two lines cut into 10 equal steps (the faint dotted lines). The end is about 7 steps along. So you estimate the next digit: 4.37.
Your estimate may be 6 or 8 and that is fine. The estimated digit is a best guess.
Do not write a digit after that. You cannot see between the imagined steps, so 4.375 would claim more than the ruler can show.
Rule: certain digits + exactly one estimated digit. All of them count as significant figures. If the end is right on a line, the estimated digit is 0 (write 2.50, not 2.5).
Show my results
Copy this onto your worksheet. It lists the 9 items from the three Worksheet Sets.