Increment action in conditional actions

Would I be correct in saying that the way to "increment" in conditional actions is to do the following:

expression var_1 = var_1 +1

Specifically, I am trying to make a sort of progress bar. the user edits sentences and IF it is correct I want var_1 to increase by 1. At 5 the image is a dark lightbulb. at 10 the image changes to a brighter lightbulb. at 15 still brighter etc etc.

So at every multiple of 5, I hide/show - IF var_1 is equal to 5 - 10 - 15 - 20

Just wanted to check and see if my workflow is faulty

Thanks agains to the usual suspects (rod, lilybiri, rick et al)

John