The actual length of a machine is 12.25 cm the measured length is 12.2 cm

Since p=q/w or percent equals quatity divided by whole, u have to divid 12.2 by 12.25

First, calculate the difference between two length. The difference is the error of measurement.
the difference = actual - measured
the difference = 12.25 - 12.2
the difference = 0.05

Second, calculate the percent error
To calculate the percentage, we will use the following method
percent = the error measurement/actual measurement × percentage actual measurement (100%)

Third, input the number
percent = 0.05/12.25 × 100%
percent = 1/245 × 100%
percent = (100/245) %
percent = 0.408 %
percent = 0.4 %

Percentage of error is 0.4%