Broadband Speed Test

Does the broadband speed test measure the speed to the router or to the computer? I'm getting hugely varying figures from two wirelessly connected PCs, from different rooms. I've been having internet connection issues and want to know whether these speed variances can be accounted for by the location/equipment of the two PCs or whether they are actually speed fluctuations in my line?

Speedtests will measure the speed to source to computer.

Using wireless is NOT the way to do a speedtest. Because wireless can vary so much in throughput - with distance, interference, standard &c, you are unlikely to get an accurate result. You must undertake tests using a wired connection for the results to be in any way meaningful or for use in any comparison.