Mouse tracking does not work for large ranges in one of the axis.
I tested with yaxis values between 0 and 20, and xaxis values between
someDate.getTime() and (someDate plus some days).getTime()

What steps will reproduce the problem?
1. Create a chart with data like:
[0.11, 90000000],[0.15, 1000000000],[0.2, 20000000], ....
2. The tracking of the mouse will not work correctly.

What is the expected output? What do you see instead?
Probably the mouse will be tracked within the first or the last point, but
not for the other points.

What version of the product are you using? On what operating system?
v0.5beta and Prototype (1.6.0.3). OS: Ubuntu Hardy

Please provide any additional information below.
I solved the problem adding different sensibilities for each axis.

In Line 186, intead of:
 185                                 trackDecimals: 1,
 186                                 sensibility: 2,
 190                                 radius: 5,

I have:
 185                                 trackDecimals: 1,
 186                                 sensibility: {
 187                                         x: 2,
 188                                         y: 2
 189                                 },
 190                                 radius: 5,

Then you have to change lines:
2440  xsens = (this.hozScale*this.graphData[i].mouse.sensibility);
2441  ysens = (this.vertScale*this.graphData[i].mouse.sensibility);

with:
2440  xsens = (this.hozScale*this.graphData[i].mouse.sensibility.x);
2441  ysens = (this.vertScale*this.graphData[i].mouse.sensibility.y);

hope it helps!
Marcos.