Subject: how to get measurable data

  I am testing to see if bacteria in solution increases the rate of rust on 
iron.  My teacher wants measurable data.  I think I could weigh the nails to see 
if there is a change in mass and that may indicate the rate of rust.  Do you 
have other ideas on how I can measure?  I am limited on time because my first 
project did not work.  Please help!

Re: how to get measurable data