Ovulation microscope

Anyone else use a microscope to check their saliva for “ferning”. I’ve been checking it every morning when I first wake up like it recommends. On Sunday I started to see some ferning and then again on Monday. On Tuesday and Wednesday there was no ferning at all. I know I didn’t miss ovulation because I’m also using an OPK and there has only been a very faint line. Am I doing something wrong with the microscope?