Force first three characters
I have an IRD field 11 char long whose first 3 characters are always R00 followed by 8 digits.
But how do I use an input mask to force the 2nd & 3rd characters (the zeros) There’s nothing in help for that. Please advise.

If they always have been and always will be R00, you can just put "R00"(rest of input mask) in the Format field of Properties.
If not, then I'd suggest perhaps having another field with a default value of R00 and concatenating the two in display view. Then you can change it in the future should circumstances change.

HTH,
David R

thank you! it worked!