The first day I was first exercising until 3 first, and then 5.
The second day I was able to reach 5 or 6 every time, and then after half an hour I'm sometimes able to reach the 9!
The mnemonic technique I'm using is that instead of memorising the positions of the numbers, I memorise the path from number 1 until 9. I memorise it as a kind of drawing/shape.