Total beginner, dynamic related table?

Hi 

I have my dataset with a numeric value.

This can either be less than or equal to 0 - then its "On time". Else its delayed.

The values can be from -2 -> what ever. So instead of mapping every value.

I was thinking to create a table based on a formula?

So 
IF
Completiondiff <= 0
THEN

"On time"
ELSE
"Delayed"
ENDIF

But I have no clue how to do this in power bi? I tried adding a meassure, but i could not find the syntax?