Gerd Lensing, Characteristic marks on the optical apparatus of the Army
Kennzeichnung von optischem Geraet der Wehrmacht
Mitteilungen fur Freunde und Forderer.  Museum fur historische Wehrtechnik 
   e.V. Nurnberg,  Ausgabe 15, S.29-31, (1987)


Optical equipment of the Army carries a number of inscriptions and 
characteristics of different meanings.  Adjacent to the information about 
the manufacturers (coded or not,) instrument number, or technical data, 
there are some additional marks, for example crosses or triangles, whose 
meaning is described in the following.

Weather influences, especially extreme cold, affected not only vehicles 
or weapons.  Instruments and equipment were confronted with degrees of cold 
that had never been experienced before, especially at the Eastern front.  
The fine mechanical adjusting devices, as found in optical instruments, were 
especially prone to become difficult to move or completely stuck with 
increasing cold.  The fine threads in sensitive focusing screws could become 
heavily damaged if forced.

Inexperience led to different cold-resistant greases being adopted during 
the course of the war.  With each new measure, a mark was placed next to the 
manufacturer’s stamp, either at the factory or at the later occasion for 
repair or maintenance.  Experience with various cold-temperature greases led 
to a sequence of different markings.  Failure of one treatment led to an 
explanation for the marking that was provided with the corresponding 
restrictions.  A new, specialized grease was introduced with a new marking.  
A number of instruments are known with two marks, and theoretically there 
could have been more than two.  These optics were probably lubricated 
differently after experiences over time, and marked accordingly.  The last 
mark inscribed in a row was the correct indicator, and the preceding mark 
was not removed since the new mark included the old one.  

Often, the instrument was produced in cold resistant form by the 
manufacturer, and the corresponding marks were stamped at the factory.  The 
rarer double markings possibly indicate that the original mark was stamped 
in and the later mark etched on the cover.  

The following synopsis of marks is based on different sources and decrees 
from the Archives of the Museum and from private sources. 

The first mark used to identify treated optical instruments was the 
letters K F .  The explanation for this marking is, 'Instruments which carry 
the letters ‘KF’ close to the company name are treated with the cold 
resistant grease Invarol, which guarantees the perfect operation of the 
screws to -20 degrees C.'  (Aug. 20, 1942)

The next mark, a light blue circle, became necessary with the 
introduction of cold lubricants in larger applications and especially for 
lower temperatures.  It is explained, 'Instruments that have a filled in 
light blue circle are lubricated with Vacuum grease 1416 or a grease with 
the same cold temperature qualities.  These instruments are perfectly 
serviceable to -40 degrees C.'  (Nov. 1, 1942)

In reality, the service was probably not to specifications, since a later 
explanation was modified: 'Instruments that carry a light blue circle are 
lubricated with Vacuum grease 1416 or a grease with similar cold temperature 
qualities.  The largest part of the instrument, except for a few exceptions, 
remains perfectly serviceable to -40 degrees C.'

The existing greases very soon proved to be unsatisfactory, and a new one 
was introduced with the mark + .  'Instruments that have a light blue cross 
( + ) close to the company name are serviceable to -40 degrees C without 
problems.  (In the future, all observation and surveying instruments of the 
military are only lubricated with instrument grease 1442.)'  (Nov. 1, 1942.)

A later declaration made the following exceptions: 'Instruments which, in 
spite of the use of instrument grease 1442 or the E grease of Zeiss in the 
above mentioned temperature limits, are not usable (due to fitting or 
caulking difficulties,) carry a light blue cross.'

The final documented mark is a triangle.  There are no contemporary 
indications as to whether all problems were solved with this measure.  
'Instruments that carry a light blue triangle close to the company marking 
(letters that correspond to the company name,) are ready for use between -40 
degrees C and +50 degrees C.'

These marks were supposed to be filled in with color, but this was 
frequently not the case.  This requirement probably was intended to allow 
better recognition.  There is no explanation in the known sources of any 
special meaning for the color.

As already mentioned, the explanations for the markings were taken from 
diverse sources.  Therefore, exact dating is not always possible.  The dates 
given for the explanations are the earliest date known that the explanation 
was published.