How do I back a horse I laid earlier, to equalise profit or loss, given...

How do I back a horse I laid earlier, to equalise profit or loss, given alternative situations to trigger the bet?

I have developed the first part of my trigger to lay horses early if they meet my conditions.

I then wish to back them to equalise any profit if the price has drifted i.e. laid £5 @ 20. At one minute before the off the price is 25, I want toback it £4 giving £1 profit whatever.

OR

If the price has not drifted but the selection meets my alternative criterion, back it to equalise the loss i.e. if I have laid £5 @ 20 but the price has shortened to 18, I must back £5.56 and accept the loss of £0.56

If any selection which I laid early does not meet either of the above criteria let the bet stand and fate decides the outcome.

I have started by declaring a constant to deal with the time of the back prices i.e. CONSTANT: minutes_before_off

Please help if you can
Moose


 

I would use this expression in the amount box:

(lay_matched*bm_layavp)/back_price.

You can check the effects in this basic spreadsheet attached to see your calculation in action.  I have assigned the MF pro names to the cells in the "Back First" example but cannot repeat the same names in the lay first example (as it would mean using the same names again).

Thank you so much. I understand the maths but I have little experience of the Mf syntax  . I'll test run tomorrow.