When I put my meteorology hat aside and focus on editing, one of the most persistent errors I see is with the if/then construction when using a conditional sentence.
When one clause of sentence is only true if a condition is met (if it’s not one thing, then it’s another), the sentences need to be separated by “, then.”
I know that the “then” is typically not used in common usage, but there’s a good reason for continuing to do it the proper way: It might lead to confusion when the shortcut is taken.
I wrote a little more about it in a recent writing tip on the Administrative Information Services Web site.
If you want more information, then check it out.