I suppose I am not the first to notice this, but if you are going at say, 0.999c you will have shrunk by a factor of about 20 and everything else on the craft. Suppose the spacecraft is 2000 meters long, at 0.999c it will shrink to about 100 meters long. So suppose a person 2 meters tall, 2000 mm, standing up, is now 100 mm high. So suppose you have a 2 meter ruler. If you hold the ruler upright (aiming in the direction of travel) it is now 100 mm long. BUT if you now move it 90 degrees, now aiming at the sides of the spacecraft, it will now have grown back to it's full 2000 mm. That suggests you can make a speedometer by just having 2 rulers at 90 degrees off, one pointing in the direction of travel and one pointed sideways. You would be able to see the sideways ruler is still 2000 mm long but you would also see the up and down pointed ruler at 100 mm. So having a chart, you could figure out your velocity by seeing the difference between the two rulers! Is there something wrong with this scenario?