Hi Nat,
Here's the way I do it (I trade with Oanda and have to convert the P/L numbers to pips manually
because of their lousy transaction history):
1. Determine your "Base Lot Index" which is the % of the account you trade. So if trading X% of your account is 3 lots, then
3 is your "Base Lot Index".
2. In order to calculate the pips gained (relatively to the trade size) use the following formula:
Pips(adjusted) = Lots closed * Pips / "Base Lot Index"
In your example, you closed 1/3rd of your position at 20, 1/3rd at 80 and the rest at BE so you gained:
(1 * 20 / 3) + (1 * 80 / 3) + (1 * 0 / 3) = 33.3 pips
Note that if you multiply the result by the "Base Lot Index" you get the "absolute" pips: 33.3 * 3 = 100.
Astro