Get directions, maps, and traffic for Prospect Park, PA. Check flight prices and hotel availability for your visit.
GPS satellites carry atomic clocks that provide extremely accurate time. The time information is placed in the codes broadcast by the satellite so that a receiver can continuously determine the time the signal was broadcast.
How does a phoropter work (mechanically)? There seem to be some really neat gear/clutch mechanisms at work throughout the device, what are the actual mechanisms involved? For instance, how does the axis adjustment knob adjust all the astigmatic lenses and the cross cylinder at the same time? Or how does the fast sphere knob work?