Hi
Are you sure that Excel is the kind of tool you need for this?
It seems like having a web-based (I don't mean online out in the wild - but something hosted on a computer on your local network) user interface might be more appropriate.
The UI would basically be a webpage accessible from your browser (again, only from inside your office with appropriate user credentials - nothing is out in the open). All the data would be held inside a database.
You could keep track of your injections, when the last injection was made, quantities available, and so on.
The nice thing is that you just stored the information as a series of transactions (think of it like stock - you put stock in, then take stock out - each time you do that, you record a transaction). To get the total stock on hand you just do a quick sum of your entries in the DB.
Anyway, if you want to talk more about what you require and suitability and so on, just send me a message. But really, Excel seems like the absolute worst tool to be keeping track of this (you just get concurrency issues - e.g. if 2 people use the sheet at the same time, or 'let's make a copy of the sheet' issues to deal with). There's really a much better way to do what you want.
Thanks a lot,
John