It is worth noting that I did not get a alt-text at all on OS X/Safari OS X/Firefox XP/Chrome or XP/IE8 (non compatability mode).
The alt-text is clearly in the source however, it is equal to the bars height in pixels (the graph is 103 pixels tall [and I believe it has 3 pixels of white space] so it just uses a 1%=1 pixel translation). Since the graph is labelled as to its top speed then I would interpret your examples as follows.
61% * 200K = 122K
134% * 200K = 268K
That said, I would not trust this graph in any way, it is a rough guestimation and not meant for serious bandwidth monitoring.