What's my weight?

I've fought against the inevitable ups and downs of weight control my entire life.  Because of this, I'm very concious of how much I eat and how much I exercise, but I'm never keeping good track of the day-to-day variances in my weight.  

I would like to have an application that allows me to enter my weight at certain periods of the day (morning, evening, before and after exercise, etc.) so that I can have a reliable partner to track how I am doing over the short-, mid- and long-term.

At this point, I've decided to limit tracking to 4 items per day; morning, evening, before and after exercise.  This will allow me to have sufficient data without making the app too complicated and onerous to update.