Hi Richard,

yes I did.

But the input is not always digits/numbers alone and the place of the
letters can change at every single input.

They can be at the beginning: YZR1234, result YZR-12-34,
in the middle: 12YZR34, result 12-YZR-34.
Or it can be only 2 letters: TA1234, result TA-12-34.

An input of TA123 should return TA-12-3, where
an input of TA12345 should return TA-12-345

I think it's hard to put all the possibilities into a 'telephonish'
calculation format.

That's why I made the CF years ago, to first isolate the digits and put back
the rest of the input at each iteration.