How can I measure my productivity when using multiple devices? I'm a software developer, and I typically work in several virtual machines during the day. Is there a tool like RescueTime or TimeSnapper that will allow me to analyse my software usage across multiple PCs? Or do I need to consider a different approach?
The work time is usually limited to a similar amount every day but time is not strictly related to productivity. I personally understand productivity as a standard output unit over time, meaning a higher output in the same time interval suggests an increase in productivity. Taking for example an industry employee who's supposed to pack boxes: if he manages to increase his packed-boxes/hour ratio he can technically work for less time to deliver the same work.
However, due to the variety of activities that can be developed in other businessess, it can be hard to set a standard unit to report whether the productivity has gone up or down. I suggest reading the Pomodoro Technique to understand how they use blocks of 25 minutes (aka pomodoros) to gather information regarding focused time. The biggest drawback of this unit is you'll probably have to adopt the whole system to use but who knows? You may even like it.
The picture above shows a sample of a simplified record sheet that you're supposed to do by the end of each day. It gives a good overview of how much focused time you managed to succesfully use. If you happen to stumble upon an undelayable task or notices something interrupted you for too long, it's very likely that you'll have to void the current pomodoro.
But why 25 minutes?
Cirillo, Franceso. The Pomodoro Technique. PDF Version. 2006. Page 6, §4.