Formula used by Excel to determine y-axis interval in chart

[M Chin]

Where may I find the formula used by Excel in deterining the interval for
y-axis when converting data to chart

 

[Jon Peltier]

The min and max are fairly well characterized in terms of the major tick
spacing:

http://support.microsoft.com/default.aspx?kbid=214075

I have found no published information about how Excel determines the major
tick spacing.

- Jon