Possible Duplicate:
Why did the Star Trek writers decide Warp 10 would be infinite?
In TOS (I forget the episode) but with some help enterprise reaches warp 13 (or something significantly greater than 10).
Yet in TNG the Warp scale is supposed to top out at 10 (being infinite or something like that). Several times you see the Enterprise-D straining at 9.x but it never reaches 10.
Was there a re-calibration of the Warp-Scales in the intervening 200 years?
Or some other explanation for the differences in scales.