Excel vba that counts days when condition is met and put the schedule in the calendar.

[saman018]

Hello,
If someone could help me, it can be vba or just formula in excel. My dilema is to make a scheduling calendar that tracks the frequency of lab test. For example, normally test should be done every three days, which will be recorded in the calendar. However, if for 20 days, the tests seems okay then the test can be done in every week, changing the the schedule in the calendar.
Please somebody help me.