The short answer: It removes the trailing newline from $scaler.

The long answer from perldoc.com:

This safer version of /chop removes any trailing string that corresponds to the current value of $/ (also known as $INPUT_RECORD_SEPARATOR in the English module). It returns the total number of characters removed from all its arguments. It's often used to remove the newline from the end of an input record when you're worried that the final record may be missing its newline. When in paragraph mode ($/ = ""), it removes all trailing newlines from the string. When in slurp mode ($/ = undef) or fixed-length record mode ($/ is a reference to an integer or the like, see perlvar) chomp() won't remove anything. If VARIABLE is omitted, it chomps $_.