but why do we say "Changing to Wherever on one three three decimal one five zero"?
Have a read of the latest CHIRPS. A pilot there confesses to having copied a frequency down wrong on his pre-flight planning. On changing to this wrong frequency he created an issue for himself and a potential hazard for others. The purpose of stating the agency
and the frequency that you're changing to is to give an opportunity for the agency that you are about to leave to cross-check you have the correct information. We had a period of about 3 years after the local RADAR unit changed its frequency where departing pilots were stating the old frequency. I'm sure we saved some people from calling fresh air.
The requirement to say 123.5 instead of 123.50 was introduced a few years ago to get us used to the phraseology required for 8.33 kHz channel spacing, along with (more importantly) saying 134.050 instead of 134.05. I like the habit of finishing the call with my callsign, so that's where the transmission would get clipped, if anywhere.
TOO