Finally sorted out how to add conservatism to the software. now running at 85% M values and 60% max gradient factor. May give the user options to change these one day. Seems to give very similar profiles to m-plan and vplanner.

25m dive on air 30 mins bottom time square profile descent 15m/min ascent 10m/min
1min at 9m
2m26s 6m
12m32s 3m

output looks like this for all % m values , profile and predicted ascent time.

Hardware platform now developing too. Turns out olimex make a very nice small pic board called a pinguino-OTG which includes a realtime clock , SD card slot and lithium ion battery mangement kit. Just need to add the screen and sensor and a battery ant its ready to dive.

nice things about this is it is 32 bit with lots of program space (32kB) and 8kB of RAM. Should be less of a problem to fit the code into this thing.
Will need a fairly big box though - board is 69mmx54mm .