Having completed my skills test (finally

) I am about to do my Nav test - this weekend, weather permitting.
I have a question for all those who have already done the Nav Test. When it came to your diversion, did you estimate your new heading and new ETA in your head (possibly based on the 3000ft winds at take off), or were you permitted to use your CPR-3 flight computer during the flight ? to calc/est them
I am slightly confused as my instructor said I could use the CPR-3 and then the following day told me he'd prefer it if I didn't !
Anyone have any comments ?