Axis scale on X-Y scatter graph

[Guest]

Is it possible to link the scales for the X and Y axis so that the scale can
increase/decrease automatically, but both X and Y always cover the same
range. I am plotting data which is just easier to read if 0,0 remains in the
centre of the graph - I could fix the axis scale, but I want to leave as
'auto' due to the changing data.

Thanks,

Andy

 

[Del Cotter]

Is it possible to link the scales for the X and Y axis so that the scale can
increase/decrease automatically, but both X and Y always cover the same
range. I am plotting data which is just easier to read if 0,0 remains in the
centre of the graph - I could fix the axis scale, but I want to leave as
'auto' due to the changing data.

I would suggest creating an invisible data range consisting of four
scatter points whose x values are plus and minus the MAX() values of the
real x values, and whose y values are +/- the MAX() of the displayed y
values.

x y
MAX(x-range) MAX(y-range)
-MAX(x-range) MAX(y-range)
MAX(x-range) -MAX(y-range)
-MAX(x-range) -MAX(y-range)

This invisible rectangle should, if I'm right, keep your automatic
ranges centred on the screen.

 

[Guest]

Del has the right idea but you need to use a more complex approach. Instead
of just MAX(x-range) use MAX(MAX(x-range),ABS(MIN(x-range))) This will cater
to the possibility that the -ve values have a larger absolute magnitude than
the positive values.

This *should* give you (0,0) in the center but one cannot be sure since XL's
algorithm for calculating the axis scaling is not documented (at least the
last time I checked it was documented for XL5 and not for any later version).
--

Tushar Mehta
http://www.tushar-mehta.com
Custom business solutions leveraging a multi-disciplinary approach
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