Hi
I don't think you can compare the price difference in one refresh to the price 1min before the off, so I've done it on one refresh only.
lay price difference over 1 refresh = l_growth
percentage difference according to google: "First: work out the difference between the two numbers you are comparing. Then: divide the difference by the original number and multiply the answer by 100."
so I think your condition for 40% decrease in lay price over 1 refresh is:
and selections trigger expression l_growth/(l_growth+lay_price)*100 is equal or less than -40
please use test mode when testing it.