A couple of years ago I had a simple plugin or hack and I can't remember what it was.
Basically, beneath each post on the write post page was a box where I would enter a number. This was for my blood sugar. Then it would take that number and
If it was over 200, print red.gif
if over 150 print yellow.gif
if over 100 print green.gif
if over 70 print yellow.gif
else print red,gif
So the output looked something like:
Blood Sugar is 125 (green.gif)
And that was printed just below the post, inside the loop.