X00000009B, Y00000009B, Z00000009B This historical serial #000000009 "Experimental Set" of Silver Certificates. The entire first three packs of each block (X-B, Y-B and Z-B) were purchased by Aubrey & Adeline Bebee in the 1950s and closely held until they finally decided to sell off them in three note sets. The first major experimental group of small notes was printed in November 1932 and delivered to the Treasury for release into circulation January and February of 1933, during the period of the $1.00 Series 1928A and 1928B. The experimental set was to determine the effect of changing the relative amounts of linen and cotton fibers. The X-B and Y-B groups were each printed on paper of different portions of rag content with the Z-B group as the control, using the distinctive paper in regular use. $1 1928B Silver Certificate X00000009B PCGS Graded Very Choice New 64 $1 1928A Silver Certificate Y00000009B PCGS Graded Choice New 63 $1 1928A Silver Certificate Z00000009B PCGS Graded Very Choice New 64