Google Math (with applications to physics)
The google search box can do some crazy things. One function is being a calculator. Try typing in 2+2
Basic stuff, right? Well, it can go a bit beyond that. Next try typing in "seconds in a year"
An approximation for this, taught to me by Dr. Phil Kesten at Santa Clara University is pi * 10^7 seconds
Even more complex is typing in something like Avogadro's number and multiplying it by the mass of a proton to get the approximate molar mass of Hydrogen
These functions were quite useful for calculations even in my physics classes. Play around with it, not everything will work, but many calculations will.