Speedohealer calibration percentages?

Hey I was wondering if anyone knows what number I should use to input for the speedohealer (not the DRD one, but the healtech speedohealer).

Using the online calculator app, inputting these settings:

Compensate for factory error: Yes

Sprockets
Factory: 13/43
Current: 13/47

Tyre of speedo driving wheel 
Factory: 120/80-18
Current: 120/90-18

For the driving wheel info, I simply read the numbers off the stock rear tire and off the Dunlop D606 which I have now.

Inputting this info, it output a calibration of -10.1%.

I'm not quite sure how accurate this is, and I was wondering if anyone has already came up with the correct calibration number. I know I'm using a popular rear tire and sprocket setup, so I'm sure someone has already determined this number.

Thanks a lot!

PS - I also have 17" street tires which I will be swapping out for when I go on road trips. I will be keeping the 47T rear sprocket though, so only the tire will change. This will be my second stored setting for the speedohealer. So if anyone knows the calibration number for that one as well, it would be greatly appreciated!