Hi
if it's expected profit
you would probably need to record that in a user variable, say expected_profit and then use:
expected_profit*0.10
this example trigger demonstrates similar by remembering the expected profit from another market and using a percentage of that
if it's profit from the last settled market you could use last_pl variable:
last_pl*0.10
please test using test mode first
edit: also have a look at tradeout_net variable:
tradeout_net*0.10