Note: keywords in Bold in the following.
In Col O & P (Odds & Stake) I've set these to be populated only if either BACK or LAY is shown in a cell in Col. N (Trigger). The formulae I have in Col. N is triggered by any 1 of 3 scenarios I have set-up.
Because Col. Q to U are in effect 'Cell Inputs' I can use these without causing any 'Circular References' in EXCEL.
Now, if a cell in Col. N shows BACK, the Odds & Stake (Cols. O & P) will be populated, the bet will be fired-off to Betfair, the cell in Bet Reference (Col. Q) will show PENDING, and when the bet is matched this will will change to, is it MATCHED??!! I've set the formulae in Col. N to change from BACK to HOLD as soon as the bet has been fired-in to Betfair, by using PENDING in Col. Q to change Col. N from BACK to HOLD, to avoid bets being continuously fired-in to Betfair. In effect no further bets will be made until the last bet has been Matched, and Col. Q shows this by changing from PENDING to MATCHED??!!
If you can understand the above

1) BACK or LAY in Col. N triggers a bet to be fired-in to Betfair. (Yes/No??)
2) The Odds & Stake entered in Cols. O & P are what is fired-in to Betfair. (Yes/No??)
3) When the bet is received at Betfair the relevant cell in Col. Q is populated with PENDING. (Yes/No??)
4) When the Bet is Matched at Betfair the relevant cell in Col. Q is populated with MATCHED??!!! (Yes/No??) and Cols. R to U are populated with other relevant information. (Yes/No??)
5) If there is an entry in Col. N of CLEAR, then the relevant row in Col. Q to U is cleared. (Yes/No??)
Am I right with all these assumptions?
Is CANCEL, which would appear in Col. N, a keyword? If so what does it do?
Are there any other keywords?