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~ C. Plath Pedigree ~
From Franklin Instruments


Never Used Since 1974 ~ 5+ STARS

Price:  $2500.00       Shipping:  $40.00

Presented is a brand new Navy MK III sextant made by a hereto-for unknown manufacturer of Navy sextants. Our records show that M. Low of New York started making these instruments as early as 1970. As commonly believed, Scientific Instruments of Milwaukee, Wisconsin whose business dates back to about 1957 may or may not have been the second Navy contractor. That honor might belong to Franklin Instruments which made this sextant on November 1, 1974 shortly after they started
in business. However, even thought hey are still operating making electronic clocks, their founder and his son are both deceased, and their present management did not respond to our request for information about their prior sextant business.

The sextant comes complete with all its original accessories which include a sighting ring, brush, an adjustment wrench and a spare index mirror, all housed in a a Mahogany case that is finished with C. Plath hardware.

SOME BACKGROUND: A few years after the design of this sextant was adopted around 1971, I became a member of the Naval Academy’s Navigation Symposium, and remember we discussed in detail the criteria that was established for this design. They paralleled the already existing features found in sextants in the civilian maritime industry. The Navy’s design incorporating these features was late in coming since the civilian sextants were in use before WW II and were far advanced from the ubiquitous Navy’s standby during this period, the Navy MK II.

Listed are the MK III’s design features:

  • Lightweight
  • Large size index mirror
  • Large size horizon mirror
  • Lighting system
  • Vernier reading to 6 seconds
  • Handle for an ergonomic fit
  • Wide-angle telescope
  • Nonadjustable instrument error of less than 20 arc seconds
  • Military high impact absorbent case

Except for the handle and case, the Tamaya MS 733 and the C. Plath sextants met these criteria as did a few
others, but there was strong feelings in government to “Buy American” in contrast to today’s World Economy. Consequently, M. Low of New York City was selected for the MK III program, Little is known of this company other than they were in New York and in the instrument business. The sextants were made under license from C. Plath, of Hamburg, Germany who may have provided the tooling. C. Plath aficionados take note, the design is clearly the same as the C. Plath Classic sextant down to the last detail other than its ergonomic handle and large size high impact resistant case. This pedigree is noted on page 119 of the book by Friedrich Jerchow,“From
Sextant to Satellite Navigation, (1837-1987) 150 years C. Plath”.

After M. Low disappeared from the scene, Franklin Instrument of Rosboro, Pennsylvania must have become the second contractor, but this is the only example of their sextant we have seen in 35 years. In this picture is Scientific Instruments, of Milwaukee, WI. who was making these sextants as early as 1975. But they made fewer and fewer sextants as Satellite Navigation (Sat Nav), the newly accepted electronic system, became more prevalent until GPS succeeded it. SIC stayed in business until 2008 when they decided to close their doors. In one of our last conversations with the owners they told us sextants were still being made in very small numbers for newly built U.S. Navy ships at a price of $4300.00.

PROVENANCE: We were told by the former owner that the founder of a technology company, an American Indian, was given the sextant by the Navy as a token of their gratitude. The Indian kept it in storage for years, and when he met with financial difficulties he used it to pay a debt. That person sold it to us since he had no use for it.



CONDITION: The sextant shows no evidence of use . The interior of the case is new condition. Usually they are torn up in use from the legs missing the holes. The exterior has only one minor light scuff. All its machinery works well. The horizon mirror shows some age along the vertical edge that separates the clear and mirrored portion, but is still near new. A replacement is in the pockets for both mirrors, a $250.00 value. The stainless screws and clamps are bright and shiny and the black finish shows as new. The numbers match on the certificate. The lighting works. The index error is negligible, and there is a touch of side error which is a good thing. The original inspection certificate is included. A C. Plath lock and two keys are fitted to this Navy style case.

STAR RANKING: This sextant and case rates 5+ STARS

Flawless index mirror Near perfect horizon mirror
Vernier with 10 indents or each 6″ Maker’s tag
Large Mahogany wood case with hi impact interior and Plath hardware

This is fine sextant is in perfect condition and is backed by our guarantee of satisfaction. It requires someone who can appreciate the fine points of a sextant, and is willing to pay an appropriate price for this level of quality and excellence.


OUR QUALIFICATIONS: We are one of the few company’s still selling navigation instruments that know anything about them. For purposes of judging whether Joel’s opinion counts, he was the editor of the chapter on sextants of the 1977 Edition of “Bowditch”, The American Practical Navigator, NAVPUB 9; a member of the U.S. Naval Academy Navigation Symposium, 1975 -1978; the author of a book on marine sextants, Cornell Maritime Press,1975, and the founding president of Nautech Maritime Corporation which partnered with Tamaya of Japan in the introduction of their sextants and the famous NC-2 navigation computer, in the U.S. market. Joel is also a retired Master Upon Oceans, and held a U.S. Navy “D” Qualification as a Senior Skipper – Oceans. From 1995 through 2000, he served as a Varsity Offshore Sailing Team coach
at the U.S. Naval Academy.



Measuring Range: -5 to 125 degrees
Accuracy: Tested to +/- 20 arc seconds
Telescope: 2 x 40 Coated optics
Frame: Aluminum with black enamel paint and white numbers.
Micrometer Drum and Vernier Scale: reads to 6 arc seconds
Index Mirror: 57 x 42 mm with spare
Horizon Mirror: 57mm diameter with spare
3 for index mirror
3 for horizon mirror
Illumination: Yes

Weight sextant: 2.5 lbs, Weight case in case 12.5 lbs.


1 Sextant frame
1 2 x 40 Scope
1 Mirror adjustment tool
1 Spare index mirror
1 Spare horizon
1 Brush
1 Bulb
1 Mahogany sextant case with two keys
1 Certificate dated 1974
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Shipping & Packaging

The cost of shipping, packing, handling, and insurance to your destination, will be calculated point to point and is an additional charge. You may email us to get these costs. We price our shipping honestly, but we expect to be reimbursed for the nominal cost of packaging materials and handling.

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If not completely satisfied with your purchase it may be returned, if without damage, within three days of receipt in its original packaging. Return items must be insured for their full value. Only a prior email authorization by us for the return is required. Shipping charges are refundable if due to our error within the continental United States.

International buyers welcome, but inquire first. We have satisfied customers worldwide.

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Established in 2003

Celebrating 18 Years of Exellence in Nautical Antiques

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