I think my context and next actions fitted your example pretty well. What sort of highly mobile tool are you thinking of? A smartphone? You could have a @smartphone context but I find that although I CAN do a lot of things on my smartphone, It's not always pleasant. I prefer sending emails from my desk and making calls from my sofa.
Originally Posted by gtdnubcake
Often, the next action revolves around the lowest common denominator. In your example, that's the calculator or textbook.
If you have an example that fits your question better then I'll have another go.