If using multi-speed +/-, it is better to make a bit smoother acceleration - a factor 10 is dangerously high and tend to result in people either having to release/restart all the time to avoid the highest speed, or to surprise themselves when the highest speed makes them jump the target with a huge amount. If they get 100 tick too high by your suggested acceleration scale, they have to press in the other direction for 2 seconds to get 4*2 = 8 ticks, and then continue for 8 seconds more to get 8.25*10=90 ticks or in total 98. Then they must release and press for just over 0.5s to get the last two ticks. Just to compensate for a single update of overshoot.

With a more gradual speed-up, you don't get as suprised.