If you are already level at a level, then use "maintain" (but why even bother?)
If you need to climb to reach a level, use "climb"
If you need to descend to reach a level, use "descend"
Why screw about with basic English language?
Ollie A
As for the computerised system - Swanwick have the computerised system but they still tell you to report heading - why? well apart from the fact that even though each tactical controller has a planner (coordinator), for him or her to make a phone call for each A/C on a heading would be a huge, pointles workload.
But you ask why would they have to do this if it is computerised? The fact is unless the planner (who listens in on calls), actually input a symbol every time a Tactical Controller put an A/C on a heading to indicate it was under a heading instruction and similarly used the keyboard to remove the symbol every time an A/C is instructed to resume own navigation, then how is the next (receiving) sector to know that the A/C is on a heading and not it's own navigation merely by looking at the screen?