Creating spreadsheet to track fermentation data

I've created a google spreadsheet that I've been using to track my fermentations. It tracks SG compared to time elapsed, which makes it easier for me to compare multiple fermentations with the same yeast. It also calculates the SG points/hour that the fermentation has averaged. This is to help me identify if there are predictable places in fermentation where the pace slows, so I can manipulate other variables to try and keep fermentation steady.

I'm not that great with spreadsheets, so I'd love some help on tweaking this so it's perfect.

Notes & problems:

1. Sometimes I enter a data point when I change the temp, but don't take a gravity reading. Some of the calculations on this spreadsheet don't like that, but I need to keep that function.

2. I have two fermenters that I keep in the same chamber, so I keep data on both in one spreadsheet.

Here's the link so you all can see it:

https://docs.google.com/spreadsheet/ccc?key=0An4jQ6L4z8pBdFNFSzU3cXkwdkt3ckZyMjV1SU5CVUE#gid=0

i'm trying to do something similar. did you have any luck? i know this is an old thread.