Keeping a hold of max gap between dates when dates moving

A1 = 2/15/19 (and date changes daily)
A2 = 2/10/19
A3 = A1 - A2 = 5

Then A1 changes to 2/8/19 and A3 = -2, but I want A3 to "hold" on to 5 unless A1 were to move to something like 2/20/19 then A3 = 10.

I'm trying to keep a hold of the max gap between dates.

First post ever. Thank you for your time.

To do this without using "code" (VBA) you would need to enable iteration so as to permit the below, circular reference, in A3:

Formula:

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when first entering the above ensure A2 & A1 are empty, such that A3 generates 0, then enter value in A2 -- and only then start entering values in A1.

to enable iteration, go to Options -> Formulas -> Enable Iteration.