title: Excel, create an automatic save/change log, how to?
body: <p>I teach at a university and one assignment i have developed tests some quite specific modelling skill sets in Excel. Because of this, and because all assignments need to be fairly weighted, they end up having largely the same content (in terms of the final code) with different variables so that they are not exact copies - so it is fairly easy for students to take another persons completed file and input their own variables, change a few cosmetic items (drag data locations, colours, borders etc) and hand the work in as their own. i am confident that this is occurring and most of the time i can identify the suspects easily but proving the collusion (not so much detecting it), this is difficult.</p>
  
  <p>I am trying to work out how i can include somewhere on the worksheet (which i will provide as a template) a function that logs the user ID and time each incidence that the save button is pressed (or at a set interval)? This way i can have this info logged in the background (hopefully where nobody can find or goes looking for it) and it will be quite easy for me to see if at any point along the way the student working on the sheet changed - indicating collusion. Of course there are other ways around this, and i am not looking for a fail safe system, just an easy way to catch lazy cheats.</p>
  
  <p>I can find functions that save the last user to a cell, but none that can provide an ongoing log. Ideally, i would like it to be as covert as possible, i.e., avoiding obvious macros would be handy but i can understand this might be a problem. Does anyone have any tricks up their sleeve to help me in my quest to wipe out student copying? </p>