I'm not sure what you mean by a double variation, but let's review the Gray's variation. The problem is caused because the gray top of the tower -- the lantern room -- is cast separately from the top. It's supposed to have a "key" that prevents it from being put on in the wrong orientation, but somehow that key was defeated in some manufacturing process on a relatively few pieces.

The tower and lantern room have 8 sides.

Note that in the lantern room, there is a door on the 'middle level'. It's painted the same color so you have to look closely to see it. This is the KEY to the variation.

When the lantern room is put on the tower CORRECTLY, then that upper door is offset one facet to the right of the lower tower entrance door. If correct, there is a window in the upper lantern room lined up with the panel that has the lower tower entrance.

In theory the 8 sided top could be put on the 8 sided tower in one of 8 ways. In 4 of those ways, a window will appear directly above the lower tower entrance door. And in 4 more ways, no window will appear above the lower tower entrance door.

Only ONE of these combinations is correct. The other 7 possibilities are variations. And in 3 of those possible variations, a window WILL appear above the lower tower entrance door.

So the test MUST be the relative position of the upper lantern room window, not just whether or not there is a window directly above the lower tower entrance door.

Here are two pictures that show the correct (left) and one possible variation (right).






[This message has been edited by JChidester (edited 11-10-98).]