I don't know the value, but would guess it was made ca. 1920s-30s.
If you look down the page in this forum, you'll see another question about a Potthast table from Antique Lady. You'll also see some links to more Potthast information, which I include here for your convenience:
http://www.chipstone.org/publications/2000AF/2000Arthur/ArthurText.htmlhttp://www.mdhs.org/library/fotofind/PP0007fa.html