Fair And Exposition Cancellations And Precancels

Hello,

here I show some of interesting cancellations I found.
I would like to know:
- which PSS types are the three precancels on the right?
- I also found a lot of precancels reading up, but this is nothing special except for the 3 rare 20c precancels "Des Moines", "Texas" and "Detroit", right?
- is there value added to a stamp which shows such an exposition cancellation like the 4 stamps on the left? I found in Scott extra positions and values for covers with such cancellations but not for singles?

stamperix

The cancellations on the four right stamps (Scott 399, 398, 300 and 324) are not exposition cancellations but machine cancellations that included slogans promoting upcoming or current expositions. The values in the Scott catalogues are for cancellations applied at or during the exposition. These machine cancellations make your stamps more attractive, but not more valuable. The 2¢ stamp next to the two 20¢ stamps has a roller cancellation and not a precancel. The two 20¢ stamps most likely have a roller cancel also, but may have a precancel. It is more likely they are roller cancellations which hit each stamp in the same spot.

thank you very much, one thing more learned about cancellations :).

The Akron Ohio precancels are known as PSS type "L-8 E" - very common.

Thank you, too. Is there an online source just for the PSS types? I don't really need a complete list of all the thousands of precancels, but sometimes would like to know the type. I know the catalogues and also the software (installed as a trial).