#1) and #2): There is only one SI "base" unit for length and distance. It's the METER . Fractions and multiples of the METER are used to describe lengths/distance that are significantly shorter or longer than a meter, in order to avoid inconvenient numbers. They include the centimeter, millimeter, micrometer, nanometer, kilometer, etc. In the UK and many other places in the world, they use the METRE, which looks like a completely different unit, but isn't.
#3): If you watch him surreptitiously and you see that he's using an electronic balance, or a pan balance, or a thermometer to measure an object in meters, then he's not a real scientist. You can't trust any of his research conclusions, and he probably should be reported to the authorities for posing as something he's not.
On this particular list, there is only ONE item that can successfully be used to measure a length or distance and get an answer that can be expressed in meters. It is the TAPE MEASURE .