What's the standard amount of teeth front and rear on your bike? I can calculate the error.
The speedo healer only works on electronically driven speedo's, it wont work on cable driven ones (and typically they come off the front wheel so gearing changes doesn't affect them).
It alters the frequency the speedo 'sees' by adding or subtracting pulses. If the speedo sees the target x times / second the healer can change that to y times per second (hz) and the speedo will display an accurate speed.
That's a 12.1% increase (2.866 + 12.1% = 3.214). But the change is: 3.214 - 10.8% = 2.866:1 which is OEM. You can buy a speedo healer with a ready made loom so it's just a matter of plugging it in. No need to spice etc.