NoDeCo bezels from the 1960's - Dive tables question

[JMBL]

No worries, a forum is made just for that : exchanging info between geeks, and must I add the info is useless to anybody else ?

Btw, does it help in your research, have you solved the riddle ?

Merry Xmas to everybody.

 

[Flying Doctor]

Merry Christmas and a Happy and Healthy New Year too. It certainly does help. The missing piece of the puzzle is the GERS 55. So if I'm interpreting all this correctly, the earlier French Tables (GRS) were a direct Metric conversion of the US Navy tables but then sometime around 1950 onwards Cousteau and others produced the GERS 55 which went on to become the MN90

Thanks again

 

[JMBL]

I'll ask around about the GERS 55. With a bit of luck...

 

[JMBL]

Taken from "La plongée", 1955. Does it help ?

 

[lowwall]

Taken from "La plongée", 1955. Does it help ?

View attachment 876056

Looks like they are still using the US Navy Tables converted to metric.

Here's Google Translate's version:

"The U.S. Navy Diving Table, an improvement on Haldane's, is the result of the work of the "Office of Ships," the "Diving Research Section," and the "U.S. Navy Diving School."

From this diving table, validated by long experience, the G. E. R. S. calculated directly in the metric system the table given at the end of this work. It is in use in the French Navy.

A more complete theory of decompression, as well as the method of calculating diving tables, will be found later."

 

[Flying Doctor]

Thanks guys. This is great stuff although now I'm seriously confused. If this Wikipedia page is correct the US navy tables didn't change from 1939 to 1956. That means the 1955 GERS would have been using the 1939 US Navy tables.

I've attached the full spreadsheet of the 4 DOXA NoDeCo bezels SUB 300 (1967) SUB 300T (1968)

The SUB 300T Imperial is a direct copy of the 1959 US Navy tables. Even with a couple of conversion factors the earlier SUB 300 bezels are not US Navy. And even if the SUB 300 was US Navy based then why are the Imperial numbers different to the 300T.

My assumption is that the SUB 300 Imperial bezel is a meters to feet conversion from the SUB 300 metric bezel. Seems logical as the minute times are identical.

So my problem is: where are the initial SUB 300 metric numbers from. Maybe I'm missing a whole bunch of info and all the European dive tables were all based on the Haldane calculations or derivatives that were used to formulate the US Navy tables.

It seems strange to me that if the GERS 55 tables were based strictly on the US Navy tables of 1939 then why did Cousteau et al go to the trouble of releasing GERS 55 when all they had to do was translate the US Navy tables into French.

Sorry, I'm you guys are tired of me going round and round but this has me scratching my head

 

[lowwall]

Thanks guys. This is great stuff although now I'm seriously confused. If this Wikipedia page is correct the US navy tables didn't change from 1939 to 1956. That means the 1955 GERS would have been using the 1939 US Navy tables.

I've attached the full spreadsheet of the 4 DOXA NoDeCo bezels SUB 300 (1967) SUB 300T (1968)

The SUB 300T Imperial is a direct copy of the 1959 US Navy tables. Even with a couple of conversion factors the earlier SUB 300 bezels are not US Navy. And even if the SUB 300 was US Navy based then why are the Imperial numbers different to the 300T.

My assumption is that the SUB 300 Imperial bezel is a meters to feet conversion from the SUB 300 metric bezel. Seems logical as the minute times are identical.

So my problem is: where are the initial SUB 300 metric numbers from. Maybe I'm missing a whole bunch of info and all the European dive tables were all based on the Haldane calculations or derivatives that were used to formulate the US Navy tables.

It seems strange to me that if the GERS 55 tables were based strictly on the US Navy tables of 1939 then why did Cousteau et al go to the trouble of releasing GERS 55 when all they had to do was translate the US Navy tables into French.

Sorry, I'm you guys are tired of me going round and round but this has me scratching my head

I think you are thinking too hard. It looks to me like whomever originally came up with the 5m metric intervals started with the Navy table and rounded and interpolated to get numbers that he thought looked sensible.

I doubt anyone expected a table on a watch to be super accurate. For one thing, I don't believe the accuracy of the depth gauges available to regular divers at the time was sufficient to even allow precise profiles.

 

[Flying Doctor]

Thanks. Yea, trust me, I've been thinking I am over thinking it far too much but I can't get past if it was all kind of rule of thumb and rounding why are the 300 and 300T Imperial bezel different, yet the Metric ones are the same.

I think you are thinking too hard. It looks to me like whomever originally came up with the 5m metric intervals started with the Navy table and rounded and interpolated to get numbers that he thought looked sensible.

I doubt anyone expected a table on a watch to be super accurate. For one thing, I don't believe the accuracy of the depth gauges available to regular divers at the time was sufficient to even allow precise profiles.

 

[lowwall]

I just looked at some original DOXA SUB 300 bezels and it's very apparent that display considerations were more important than scientific rigour. For example, they wanted to indicate 50, 55 and 60 meters separately despite them all falling under 5 minutes on the Navy table. So they did.

Crop from the Flying Doctor's page INTERVIEW WITH THE DOXA SUB DESIGNER

In other words, the metric "table" is built from a few anchor points from the Navy tables with the rest governed by design considerations.

 

[Flying Doctor]

Hmmmm, now that is a good point because in the next generation of bezels they removed the marks at 55 and 50

Edit... thanks again. If I can't find any French tables that show 5 mins at 60, 6 mins at 55 and 8 mins at 50 then it was some jiggerypokerty with the bezel design rather than the use of correct numbers

I just looked at some original DOXA SUB 300 bezels and it's very apparent that display considerations were more important than scientific rigour. For example, they wanted to indicate 50, 55 and 60 meters separately despite them all falling under 5 minutes on the Navy table. So they did.

View attachment 876100

Crop from the Flying Doctor's page INTERVIEW WITH THE DOXA SUB DESIGNER

In other words, the metric "table" is built from a few anchor points from the Navy tables with the rest governed by design considerations.