Actual=7
scale1=7.033
scale2=6.91
scale3=7.1
which is most accurate?
also which is most precise?

The given data is
Actual = 7
scale1 = 7.033
scale2 = 6.91
scale3 = 7.1

Define 
absolute difference = |Actual - Measured|
%error = 100 * [(absolute difference)/Actual]

Note:
The scale with the lowest absolute difference is the most precise.
The scale with the lowest %error is most accurate.

Calculate absolute differences.
Scale1:  |7 - 7.033| = 0.033
Scale2: |7 - 6.91|   = 0.090
Scale3: |7 - 7.1}      = 0.100
The most precise is Scale1

Calculate %error.
Scale1:  100*(0.033/7) = 0.47%
Scale2: 100*(0.090/7) = 1.29%
Scale3: 100*(0.100/7) = 1.43%
The most accurate is Scale1

Scale1 is most accurate.
Scale1 is most precise.

It would be 18 cm

Think of it as five or above give it a shove. change the 5 or above to the right to a zero and add one to the number on the left.