Hi John
Difficult one to answer, as it depends rather on Type, Condition and Completeness. Make sure it has it's innards in place too, as they are often found as just the external body alone. Displays ok, but! Original packing tin, ampoules burster block and instructions add to the package value.
Guidelines - Mk1 or 1A complete Delay - £100 - £150
Mk II Delay - £150 plus - Far less common
Original Tin, complete except burster obviously £200 - £300 Depending
Germans may have used captured delays, as they were very partial to using captured equipment, but also had their own Celluloid Acetone Zeitzunder, Various other acid delays, and a nice selection of sabotage clocks.
Hope this helps a bit.
Cheers
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