Alright,

I just wanted to run this question by you guys because I have been trying to develop a database application for people to enter in just fitness numbers like number of pushups, height, weight, etc.  They would use a person number so that the people interfacing with the database will not see the data (but that's trivial, and I can figure that out).

What has been challenging is making it so that people can enter data at several times, and having the databse email them the percent change from their last measurement.  I know how the whole emailing thi works, and things like BMI, which are  a simple calculation are easy to email, but I am not really sure how I could get a ΔWeight or something of that sort so that I can email them that.

I guess, I'm not sure how to how to make this variable.

Any help would be much appreciated!