I'd like to have a numeric field defined to only hold (6) digits (no decimals). But I'd like it displayed as "12345-6" with the hyphen. I didn't see a field masking function, and a formula formatting does not take the current value being entered.
You won't be able to use a hyphen in a numeric field. You can however create a formula text field and set the max characters to 7 (will include the hyphen) and use a formula based on the number field you have. Here's an example:
You can call this formula text field anything you want but remember its' only a text representation of your number field and you can't do math with text unless you convert it back to numbers (but you already have the original number field).