Information is this column is from the 1921 Frederick Post Catalog as distributed by the Fuller-Peerless Company of Peoria IL.   Photocopies of the cover, foreword and slide rule pages were kindly supplied to me by someone whose name I have forgotten.  I believe this was the eleventh edition of the Post catalog but unfortunately I do not have a copy of the title page.

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.