Hi Pang,
This won't help for MIDI, as has been pointed out, but you did not specify that.
That is okay. Although ideally I want to get the MIDI to work, but for now I will settle for the score.
Here's my function for metronome marks, which allows you to use notes in them. I have a whole bunch of related functions, some with boxes, some with additional text parameters and so on. You can obviously put any number you like in here. [I have edited this a little, because I use custom had made fonts for notes and I just deleted all that for this example to help, so it may not be quite so beautiful as in my own context.]
Thank you very much for your help, Andrew, and sorry for the late reply.
I think I can see what your function is trying to do,
but unfortunately despite days of looking at the lilypond documentation,
I still have not figure out the syntax for calling a function in lilypond,
in particular I am struggling with the syntax for the arguments.
Would you kindly please show me how to call your function \metroMark?
I am pretty sure every man and his dog is going to criticise the idea of a metro mark of 72.5, as players, if this is for humans, can't attain that accuracy. No metronome I have, mechanical or digital, will let me set a fractional tempo. Just saying.
Sorry I should have mentioned that using a non-integer tempo marking is for a metric modulation in the music.
The tempo is more like a reference for the musician, alongside with the tempo relationship between the two section.