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OEM is a standard abreviation that means "Original Equiment Manufacturer". It is use to specified a manufacturer part number or standard in manufacturing something. It is lagerly use in automitive industry but applies to any industrial manufacturing frabrication processes.

As for the averager, I know the differnce between the automatic averager unit that is attach to the Mark-IX-A. It looks like a big rounded metal box that you have to wind up to activate the trigger to start the apparatus. It will run for 2 minutes, more or less (huges industries tolerance was ± 10 sec). The automatic averager was conceived to add 1/60th of the fine tuning knob value each two second.Which mean that after 2 minutes you will get 60 values that will represent a mean value reading of your time period observation. The other Mark-IX unit was a manual averager that works differently. You have to take 6 readings in a row. Each time the averager will add 1/6 of the fine knob tuning value to the counter. Between each mesurment, you'll have to pull a level that disengage the averager from the fine tuning knob. when pulling the level, you'll also have to roll back the fine tuning knob to its zero value before releasing the level for the additional reading to be add. You got a final result after 6 shots in a row. After 1941, this kind of Mark-IX unit was use solely for formation purpose since the automatic averager was finaly put in service. The manual unit was use onbard bommers from 1939 to 41. I found out that these manual unit are more accurate when well calibrated but they need about 6 to 8 minutes to be use. It takes 3 to 4 times more time to have a fix thats why the RAF as commision an automatic averager. It is a little less accurate in my opinion but more faster to get several sights reading.

My Mark-IX with a manual averager was bought from a private salor located in the Ottawa region. It came in its original case and seem to be an english unit brout from over seas. Serial number 13170/40 A.M. bubble sextant. Mark IX brit pats. 480112 490621 and pending.

The automatic one was bought from Celestaire. It came in a box with two defective units that were salvage for their parts to get a fonctional device. there was no case but luckely, a came across a Mark-IX BM empty case on sale on EBAY.UK. I bought it and add some padding to fit my smaller sextant size. serial number 2762/43 A.M. Bubble sextant Mark IX A . 6B/218. brit pats 480112 490621 and pending.

Each unit was repair following Bill Morris service munual. Some parts were bought from Paul Brewer in England. The bubble chamber was modified in order to accomodate a screw cap to ease refilling. I also have found hexane fluid to be use in the bubble chamber as it was originaly manufactured. Both unit have nice eye rubber gard and are running quite fine.

Jean