I'm looking to prodice a graph as above - basically a 3d column chart
with a variety of different values (dependent on x and y axis),
together with a plane / surface intersecting (some of) the columns. Is
basically an extension of the column - line chart, but with an extra
variable.

All the columns come from 0 to between 50 and 150 or so, but I'd like a
plane / surface intersecting the graph at 100 or so. I've tried
changing the vertical (z?) axis settings to move the intersection to
100 but then the columns come up and down from 100, instead of
remaining to come up from 0 which is what I want.

There doesn't seem to be a standard formatting function which can do
this however I know a bit about visual basic (not much!) so if anyone
can let me know some code it would be very much appreciated!

many thanks

Jonny