Marc - This is only the first of more to come.

Gwz - Do you see the calculator?
Initially a black screen is presented while the rest is being loaded (currenty 13kb).
If you don't see the calculator then it hasn't finished downloading for what ever reason. Most likely a slow connection.
Try waiting until the status bar at the bottom of your browser says Done.
Also it is possible you cought me updating the file. I continue to work on this calculator making improvements several times a day. You can now use it to figure feeder sizes by entering zeros in fields not to be included in the calculation.