I refill my two printers one an Epson RX530 and the other a HP DeskJet 720C
The epson is ok as it has a monitor but the HP hasen't. So being able to program I have created a monitor for 4 colours but would be a guide for more. It is invisable once installed. I do intend a commercial version based on feedback to handle multy printers and perhaps 5 plus colours.
It is user adjustable for fine tuning and there is now a forum for users to discuss settings and swap data setup files for a particular printer.
The place to get it is http://terry.sprinterweb.net/
Forum on contact page
I made it mainly for my HP that has no monitoring and just runs out of ink or blows a nozzle. so far it seems to record usage ok. This project is in its infantcy and I will rely on feed back via the forum to adjust the algorithem. I will update this free version to non commercial use. There will be a small fee for those who wish to use this version commercially. I can be contacted via the forum Contact page on web site above