I would say that we have to be careful talking about these measurements.
Whenever we mention any measurement, we have to say WHO measured it, because we have known for a little over 100 years that I and a person on the rocket ship will get DIFFERENT measurements for some things.
-- The person in the rocket ship claims the rocket ship is 100 m long and that my rowboat is 5 m long.
We'll assume that his meter stick, and all the other measuring equipment that he brought along with him on the rocket ship, are all good, accurate, expensive, and accurately calibrated.
His measurement of 100 m for his own rocket ship is accurate and true. It was true on the launch pad, and it's still true, no matter how fast he's going or in what direction.
But if he says that my rowboat is 5m long, then I know that it'll look longer than 5m TO ME when I measure it. We know that things appear to shrink in the direction of motion when they're in motion relative to us.
-- Similarly, if I then take MY good, accurate, calibrated, expensive meter- stick and other measuring equipment, and I measure the boat I'm sitting in AND I measure the rocket ship as it zooms by, I'll measure that my rowboat is LONGER than 5m, and I'll measure that the rocket ship is SHORTER than 100m.
