Well, not really a improvement over part 2, but now the whole instructable is listed complete on Instructables at http://www.instructables.com/id/Digital-Arduino-Voltmeter-with-Temperature/.
I go more into details on design decisions, errors that came up during the process, etc. Please vote for the project when the vote button appears. It’s been submitted to the Arduino contest, and may take some time to be accepted, so please check back. Improvements made as we use this device will be added to the Instructable.