You don't have it wrong Allen - its simply :
Start with some stock and some cash (perhaps a 80-20 split of each for instance)
Initially set Portfolio Control (PC) = stock value (SV)
Each month you check your AIM
If your PC is larger than SV, then AIM is considering buying T = PC - SV - 0.1 x SV
If your SV is larger than PC, then AIM is considering selling T = SV - PC - 0.1 x SV
Only actually trade if T exceeds some minimum capital amount, perhaps 10% of SV
Each time you BUY additional shares, increase PC by 0.5 x T (PC remains the same after each sell).
Don't trade too often, review or trade at most once each month.