actually, they didn't need examples (even if it would make things easier.)
for example, the meter was originally defined as one ten millionth of the distance between the equator and the north pole. (which, given the necessary instrumentation, was something "anyone" could measure. well, instrumentation and instruction.) it's now based on the emissions of krypton-86, and the wave length of a certain part of it. Again anyone with the proper tools is able to measure this.)
Similarly, the kilogram was defined- originally- as the mass of one liter of water. the liter was defined as the volume of a cube with a length of ten centimeters.. (today it gets quite a bit more complicated, but based on observable constants...)