@Paul_Burchfield
The Autonumber field is just that - an Autonumber field. Its value is an integer produced automatically, sequentially, and which cannot be edited.
In @Paul_Dezzutto’s formula, he is able to use the LEN() function on the Autonumber field because he is coercing the integer returned by that field into behaving like a string by concatenating it with an empty string inside the LEN() function.
Here’s his formula:
'EV-' &
REPT(
'0',
{Leading Zeros} -
LEN({Autonumber} & '')
) &
{Autonumber}
Notice that inside the LEN() function he has {Autonumber} & '' – that & '' is concatenating an empty string onto the end of the integer returned by {Autonumber}, and doing that forces that integer into behaving like a string when it gets evaluated by LEN(). So LEN() is ultimately getting the length of the value in the {Autonumber} field if it were a string.
