I was having a conversation a few weeks ago with our maintenance guy (he's a former electrical engineer) about how you would go about having a machine with a real time sales update!
Apparently you could quite easily fit 9 lasers in the lid of a machine that would measure the distance between the lid and the top of the pot in each column. It would then send a data message each time one of the lasers recorded a change via either the sites wi-fi or mobile GPS device fitted in the base of the machine. This would then add the sale to a spreadsheet on your computer.
I think the possibility of your towers telling you every time they sell a pot,or sell out of a particular line, is something I would sell my granny for!!!
The only problem is finding someone to write the relevant computer programme to interpret the signals it was getting, and then paying to convert the machines.
If I ever manage to get the maintenance guy to knock up a prototype for me I will let you know