NavList:

Dear David,

The ИАС-1(М) is a clone of this well known SOLD KM2 instrument.

The name translates as the "Integrating Sextant for Aviation", the "М" index denotes the "Modified" model. The difference between the  ИАС-1 and the ИАС-1М is:

• the mechanical "flag" appearing over the bubble chamber when the intergation interval runs out
• the bubble level is slightly different - a bigger air chamber (a small cylinder popping up from the AH body) is introduced, apparently - to prevent AH damage or leakage if the bubble left small after the sight was taken (to counter the thermal expansion of the liquid)
• several minor details of not so big significance

The "-3" sextant was for marine use, its' proper name is "ИМС-3", which translates as the "Integrating Sextant for Marine". It is said to be the further enhancement of its' aviation "brothers". I plan to buy that as well, the one obvious enhancement is the handle. The ИМС-3 has the left handle as per the Fig.2 (ref the "SOLD" article), while both the ИАС-1 and ИАС-1М have left handle similar to the one on the drum side (ref Fig.3).

All those sextants are featuring the integrators running for 40, 120 or 200 seconds.

I wish the GPS AntiSpoof could accommodate for that.

Warm regards,
Tony
60°N 30°E