Koopman chess clocks were the standard for a good chess clock.
Starting in the mid-thirties the Dutch Company H. Koopman based in Dordrecht, quickly made a name for itself. One unique selling feature apart from the obvious quality of the clocks, was the 1 or 2 year warranty period given for each clock. Sometimes even 3 years were given. Koopman stamped very often at the bottom every clock which makes life for a collector much easier when it comes to dating a clock. One caveat, the period started at the sale date, so older (type) clocks can have a later stamp-date.
