On one side is a SLIDE RULE - On the other side is a CALENDER
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With Marks:         π   MILES   GAL   KM   KT   ST   MIN   HR

Have a look at a PENDANT Versions

CHADWICK / Japan                                       (1950)

R E M A R K S :
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The CALENDER is usefull today too!    See the following EXAMPLES ...

Year 2013, July 7 = SUNDAY    ===>>  SETTING = 1963 ( see picture !)
YEAR 2014, FEB.20 = THURSDAY  ===>>  SETTING = 1951; '58; '69 or '75

impressum:
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© C.HAMANN        http://public.BHT-Berlin.de/hamann         02/20/14