Sorry didn't think that was needed to solve it.
For example lets say when my ***** is:
60% erect ; it is 6.5 inches
70% erect ; it is 7 inches
Therefore how many inches is my ***** when it is 63% erect?
10% (70 - 60) means .5 (7 - 6.5)
So 1% means .5 / 10 = .05
Then 3% = .05 * 3 = .15 : value = 6.5 + .15 = 6.65
Now be a good boy Kev, and go away...
You took a cold shower