Slide rules (catalog numbers 1400-1499) appear on pages 54 and
55 of this catalog. That implies that catalog numbers 0 to 1399 used
only 53 pages. Compare that to 179 pages in 1910 and 129 pages in
1922. Apparently Post was selling a much smaller variety of products
in 1921 than in 1910 or 1922. I attribute that to the disruption
of trade with Germany due to WWI.