No, no no... you guys have it all wrong.
The M (or m) is the Morgan, a logarithmic relative astronomical unit devised by the creators of the Sleeper Ships in honor of Joseph Morgan, a famous 22nd century astronomer. Due to relativity, distances cannot be measured with our normal units: the faster your speed (the closest to the speed of light), the smaller distances become. Therefore, your perception of distance is invalid due to your speed, and must be calculated by your ship computer, which use Morgans to cope with the compression of space.
The reason why your ship is limited to 300 K (300 000 Morgans) is because you can't go faster than the speed of light or you would become little more than energy. Of course, trade lines let you go beyond that speed because they create magnetic fields which keep your ship hull integrity intact (the same way particle accelerators work and let particles go faster than the speed of light).
Thus, when you go from 15 to 16, or 77 to 78 m/s, your speed is multiplied by the 300th root of c. Your acceleration is not linear, but logarithmic!!
See, it's quite simple!!!
NB: Yes, I made it up. It's a game, use your imagination...