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For offer a rare model of a Koopman chess clock. This one with the Patent number on the dial. The patent refers to the flag which improved the visibility of  when the flag was about to fall. This Dutch patent was submitted on the 22 of June at 24 hrs. by Dr. U.J. Rutgers living in Amsterdam. The patent was published on the 16th of January 1950 and became active starting the 15 of June 1950 and was valid for 20 years  (starting from the day of submitting, the patent would expire the 21 of June 1964, given payment of annual duties). The patent ceased to exist on the 16 of January 1958 when the patent holder did not pay the required duties. The patent describes a mechanism  on the flag together with a scale on the clock face to improve the visibility of the progress in time (to when the flag falls). Although the patent expired in 1958, a lot of clocks were produced with the patent number after that period. We can only speculate why this was done. 

This model with the seconds as colored moving disks is a rare model. The clock is in excellent condition. It stems from a period where Koopman chess clocks were considered the ultimate mechanical chess clocks available. In the Netherlands people did not say you owned a chess clock but you owned a Koopman!. Even chess clubs proudly declared that they played with Koopman clocks.  A true icon of the period. One clock isn't working.

Garantee till 1955, see photo under the clock