"John Stumbles" wrote in message
...

The most convincing way to see whether this is true is to try it! Only
needs a couple of 135degree fittings and 3 pieces of pipe. As soon as you
try to take the pipes out of the same plane the angle between them changes
from 90.

Not necessarily - you can always join two lines with a third perpendicular
to both (ie 90 degree joints) - just not necessarily where you might want to
:-)

(obviously if the lines intersect, the third line is of zero length...)

cheers,
clive