Looking for rare teeth

Stamp collectors who look beyond the shortcomings in the pre-printed stamp album search for stamps with perforation variations, among other things. And sometimes they make surprising discoveries. For instance, a few years ago, in a stamp circulation from an association, I came across a stamp priced at 15 cents from the Jubilee 1923 series of the Dutch East Indies. First, something about the perforation of a postage stamp. Sheets of stamps are perforated so that the stamps can be torn apart. Individual stamps then have 'perforation'. The perforation of the sheets is done using a perforating machine. If the machine can perforate only one row, this is referred to as line perforation. In this case, the sheet must pass through the machine twice, first vertically and then horizontally, or vice versa. With comb perforation, three sides are perforated in a single pass. Collectors and dealers use terms to indicate the type of perforation a postage stamp has. With line perforation, the number of teeth is counted along a length of two centimeters. With line perforation, the two sides of the stamp are indicated, for example, as follows: Perforation 11 x 12½. This means that 11 teeth can be counted horizontally and 12½ teeth vertically. The x (multiplication) sign is always used for line perforation. If comb perforation is involved, the : (division) sign is used. On the stamps of the Dutch East Indies, issued on August 31, 1923, to commemorate the second anniversary of Queen Wilhelmina's reign, one can encounter four different line perforations. The 50-cent stamp shown above has line perforation 11. Thus, one can count 11 perforations per two centimeters, both horizontally and vertically. For clarity, one could therefore also have noted 11 x 11. The 50-cent stamp is the only one in this series that has line perforation 11. The values ​​of 5 cents, 12½ cents, and 50 cents can occur with line perforation 11 x 11½. Thus, 11 teeth horizontally and 11½ vertically. Two different perforating machines were probably used. Perforation 11½ x 11, so exactly the opposite, occurs in the values ​​of 5 cents, 12½ cents, 20 cents, 50 cents, and 1 guilder. And that is when the discovery came! For the 5-cent value is rare. In two different circulation booklets, I found the 5-cent stamp with this rare perforation, both stamps priced at 15 cents. The catalog value is many times higher, and if one comes across an unused stamp, it is even a great rarity. The compilers of the circulation booklets had not taken the trouble to measure the perforation of the stamps and had used the lowest catalog value. The most common line perforation in this series is perforation 11½, or 11½ x 11½. The 2½ guilder and 5 guilder denominations occur exclusively in this perforation. Will you also be looking for the rare 11½ x 11 perforation of the 5 cent? More than 2 million copies of this denomination were printed in three different perforations, so perhaps you will be just as lucky as I was.