Yes - I did indeed respond thinking "Currency Meter". My error and apologies.
However, the same approach is applicable independent of the data being captured, processed, and displayed.
Only the source link and associated calculations would be different. Excluding cosmetics: colors, labels, etc..
The Currency Link via Tom's Guide is an example to work from - a template if you will.
Likewise you can use the following link:
https/developers.google.com/sites/gadgets/site_gadgets
Again work each step.
E.g.:
Link to the target site and data source.
Pull in the data.
Display data as is.
Do the computations.
Display the results of the computations.
Give it all another try and then post the results. Key is your being able to provide information about where the process is breaking down with respect to your gadget.
Post the code you use.