Hi TFO, My apology for directing that last answer to LC. When I first put this together back in the late '80s here's the formulae I used for predicting the next buy and sell prices for AIM:
NSP - Next Sell Price
NBP - Next Buy Price
SO - # of shares owned
MSO - Min. # Trade Shares/Order
PC - Portfolio Control
NSP = ----------------------
SO (0.9 - (MSO/SO))
NBP = ----------------------
SO (1.1 + (MSO/SO))
This assumes that Buy and Sell SAFE are 10%. If you are using Split SAFE, then change the 0.9 or 1.1 accordingly. For instance, if you are using zero SAFE for selling, then it would change to 1.0 from 0.9. If you are using 20% Buy SAFE, then it would change from 1.1 to 1.2.
Note that these predict the price/share at which the minimum share transaction will be satisfied. These can be modified to calculate the price/share at which the minimum dollar amount is satisfied.
These might work better than Santos' formulae his "My Adaptation of AIM" image.
Let me know if you can fit these into your spreadsheet. I used these as far back as Lotus 123, so am confident you will be able to adapt them.
While they seem simple enough, it took me a while to get them right. I'd made it much too complicated at first and only going away on vacation and getting my mind off of it helped!