Keep value in cell after conditions met

[rvfotoproducties]

Hi,

I have problems finding the right formula. I want to keep the date in a cell. The date in the cell depends on certain conditions. Once the condition is met, the date of that moment must be given. This is not a problem in itself. The value that is checked on, however, changes. I do not want the date that has already been generated to be redefined but the old date to be retained.
E.g. On Tuesday, cell A2 = 70
B2 checks the date of the day on which 70 or more has been reached = If (A2> = 70%; TODAY (); "") and gives, for example, 5 March 2019
On Wednesday the value A2 increased to 75
On cell B2, the old value must remain 5 March and may not change. No idea how to do this.
Can anyone help me with this?

Thanks in advance

Regards
Ruud

[FDibbins]

Short answer - you cant.

If you have a cell with a formula that references A2=70 and does some calc, if A2 then changes to 75, that cell will recalc based on the new A2 value - the old A2 value no longer exists

[regaudio]

I would put previuosly an "AND" function between A2 and the cell to host the date that should be different form "".Then if the "AND" is false I would skip the date