Koopman        

One of the earliest Koopman chess clock, dated from 6th January 1936: still classical “old-fashioned” hands as well as 3-lines Manufacturer logo (exactly the way it was advertised in the Dutch magazine Damspel 1936). There are 2 owner signs: 1. 'Bureau voor de industriele eigendom' (=Hague Patent Office, an org. stamp) 2. 'Dr. W. Euwe' (an inscription, made by pen). It might be the case, that this clock belonged to Dr. Willem Euwe (brother of Max Euwe), who worked as Engineer in the Patent Office and was also a chess player. Photo: Alex Vinken vs. Max Euwe (Maastricht, 1946).

This is a small pre-war Koopman, dated back to 1937 (what evidences the stamp on the bottom). The Advertisement in the Dutch chess magazine (1937) defines this Model under the number '3' (the smallest and objectively the cheapest clock) being the only model without a second hand (which is also stated explicitly in the Ad). This clock could be recognized from the game between Max Euwe and Haye Kramer (Hotel Zeiler in Baarn, 1941).

Another pre-war model, dated back to 1939. Label 'VAS' identifies 'Vereenigd Amsterdamsch Schaakgenootschap' or simply saying United Amsterdam Chess Society. This model could be recognised from the game between van Sheltinga vs. Donner (Beverwijk, 1950).

Another early Koopman (1940) with HAC-like clock movement (looks like a HAC, but seems that not: construction is slightly different, also missing whatever production mark, including traditional "W19"). This modelcould be recognised from the game Efim Geller vs. Kick Langeweg (The Hague, 1962).
 

Later Koopman model, dated back to 1953. I believe it is the most widespread Koopmant clock in post-war times. Photo: T.Petrosjan vs. H.Donner (Netherlands, 1962).

Small Koopman (21cm x 11cm) with German movements and a guarantee stamp until 1957. Most remarkably that all clocks of this type have a guarantee till 1957 (at least what I saw), which may mean that this model has been produced only shortly around 1955. There was no far and wide usage of this Koopman clock in big chess tournaments (maybe small and respectively slightly cheaper clocks were designed more for home / private usage?), however one evidence still exists: Jan Hein Donner vs. Max Euwe (Netherlands, 1958).

Koopman model with Jerger 'Hearts' clock movement, dated back to 1959. It could be recognised from the game between H.Neunhoffer and R.Hartoch on some chess tournament in Hague (1963).
Late Koopman chess clock: classical post-war design with slightly simplified and clear clock faces, making them look more conservative. Guarantee stamp till 1962 means that it was produced in 1960. Movement W22 differs from the other movements used by Koopman, its supplier is unknown. This clock could be recognized from the games of Laszlo Vadars on International Youth Tournament (Groningen, 1965) or Max Euwe vs Karel Opocensky on Reti Memorial (Bladel, 1969).

Koopman model with unknown clock movement, dated back to 1965. Photo: Bent Larsen vs. Lajos Portisch (Rotterdam, 1977).