Thanks for the tips on making shell trays, Andrew (Grebneff, that is...
there are getting to be a lot of Andrews on this list). I'd just like to
add that the dimensions of standard chipboard trays are designed so that
they fit together neatly as Golden Rectangles. Golden rectangles have the
pleasing property of maintaining the same ratio of width to length, no
matter how many times they are folded in half. For example, standard
American stationery (8.5 x 11 inches) and most American books are in the
form of a Golden Rectangle; standard European stationery ("A4 paper") and
most European books are narrower and taller. I have no idea how the
dimensions of A4 paper were decided upon.

So, if you double the area of any tray, you get the next tray in the
series, as shown here in American units. The trays should be about 5/8
inches tall.

1.5 X 2 inches
2 x 3 inches
3 x 4 inches
4 x 6 inches
6 x 8 inches

The same ratios will work in any set of measurements. What are the standard
sizes for metric trays?

Andrew K. Rindsberg
Geological Survey of Alabama