Good morning, David. Access did not randomly convert =Avg([BloodPressure]) into that much more complicated expression on its own. Something had to save a design change to that control - either an accidental edit in Design View, VBA code that modifies ControlSource, an import/restore of an older object, or possibly database corruption. That exact expression looks like someone was trying to calculate separate averages for the systolic and diastolic portions of a value such as 120/80.

Also, =Avg([BloodPressure]) will only work properly if BloodPressure is a numeric field. If BloodPressure contains text like 120/80, Access can't average it as a single number. The longer expression is attempting to split the text at the slash and average each side separately.

The bigger issue is that BloodPressure really should not be stored in one text field. I would use two Number fields instead:

Systolic
Diastolic

Then your footer controls are simple and reliable:

=Round(Avg([Systolic]),0)

=Round(Avg([Diastolic]),0)

And if you want to display them together:

=Round(Avg([Systolic]),0) & "/" & Round(Avg([Diastolic]),0)

For now, make a backup copy of the database first. Then check the affected footer controls in Design View and look at each ControlSource property. If they all suddenly changed, I would also run Compact and Repair Database. But I would be very surprised if Access itself generated that particular formula.

Blood Pressure Field is set as a Text Field, and it appeared to work just fine until I entered this mornings readings, then, boom!, it was broken. I do not rember doing anything other than enter today's data.

That makes sense. The expression probably encountered a value that it couldn't parse correctly this morning. For example, a blank BloodPressure value, a missing slash, extra spaces, or anything other than the normal format such as 120/80 can cause InStr, Left, or Mid to produce an error. Once one record causes an error, the aggregate calculation in the footer can show #Error.

Open the table and carefully inspect today's BloodPressure entry, plus any records entered around the same time. Make sure they all follow the exact same format:

120/80

No blank values, no extra text such as "120 / 80", and no entries like "120-80".

That still doesn't explain why the ControlSource itself changed from =Avg([BloodPressure]) to the longer formula, because Access would not make that change just from entering data. But the longer formula is likely what is now failing because of a bad or unexpected BloodPressure value.

Ultimately, splitting this into Systolic and Diastolic Number fields will eliminate this whole class of problems.

Watch Fitness 66 where I actually set this up.

Thank You!