Type 21 chronograph program

Ministry of national defense and armed forces
State secretary to air armed forces
Aeronautics technical and industrial department
Aeronautics technical service
Equipment section

LD/JT

Eq 231-30

Technical program for type 21 chronograph wristwatches destined for use in flight

No. 231 - 30 / Eq

Document structure

Pages Nos. 1 to 9

April 1956

Chapter 1
Program objective

This program is destined to letting known the goals which will be sought after in establishing the chronograph wristwatches destined for use in flight known as "type 21 chronograph wristwatches"

The conditions appearing in this program are not mandatory, but will serve as a reference while writing the rules related to this type of instruments.

Chapter 2
Construction characteristics

The type 21 chronograph wristwatch is a watch with a case entirely made of steel, with screwed back, has a diameter of approximately 37 mm and has two lateral bridles in which can be attached two small leather bands to be fastened around the wrist.

All parts of the instrument are especially designed to being used in flight: resistance to shocks, to extreme temperatures, to sudden low pressures…

2.1 - The movement

2.1.1 - Comprises efficient anti-shock and anti hairspring sticking apparatuses

2.1.2 - Is of good quality

Minimum required quality specification

• 10 synthetic jewel holed stones, comprising at least that of the balance wheel, with a domed olive shape
• 2 synthetic jewel endstones

• 10 synthetic jewel holed stones, comprising at least that of the balance wheel, with a domed olive shape
• 2 synthetic jewel endstones
• anchored setting made with care (beryllium steel, synthetic jewel lever and ellipsis)
• mainspring with clinched or welded flange
• mainspring arbor on four polished pivots
• Operation time of 35 hours at least without winding

2.1.3 - Shows no defect

Are notably considered defects: stain or scratch, parts not carefully deburred, off-centered hairspring regulator, any defect on the chronograph mechanism…

2.2 The case

2.2.1 - Holds a mobile bezel with a radioluminescent indicating mark which can be placed, by a rotation, facing and as close as possible to any marking of the main dial.

2.2.2 - Is carefully made, with the closing system, glass and crown adjustment ensuring a perfect dust protection and a humidity protection which is sufficient to avoid mechanisms corrosion for a long time, even under very wet atmospheric conditions.

2.2.3 - Shows no defect

Are notably considered defects: stain or scratch, defective encasing…

2.3 - All dials have a black background color, solid with a main dial and two small secondary dials.

2.3.1 - Main dial (watch) peripheral scale with 300 divisions identified by white lines especially visible at each 5 divisions; each 25 divisions, double numbering.

• one with large radioluminescent numbers, in hours from 1 to 12
• the other with small white numbers, in seconds from 5 to 60. Numbers 6 of the hours and 30 of the seconds are facing the strap.

Radioluminescent hour and minutes hands; seconds' hand also radioluminescent on its tip on a stretch which is sufficient to ensure a good night time legibility.

2.3.2 - Secondary dials

• one, in place of the 9 hour digit is the small regular seconds dial; scales with 60 divisions marked by more visible white lines at every 5 divisions; every 10 divisions, numbering in seconds from 10 to 60, in white, white hand.
• the other, in place of the 3 hour digit, is the running chronograph totalizer dial; scales with 30 divisions marked by white lines; every 5 divisions, numbering in minutes from 5 to 30, in white. White hand.

2.3.3 - Across the black background of the main dial is readable the inscription "chronograph watch (X) type 21" (X being the manufacturer name or brand).

2.3.4 - The dial-hands group shows no defect

Are notably considered defects: scratches, defective handing, off-centered dials…

2.4 - Controls are performed thusly:

2.4.1 - Movement winding and hour setting with exterior grooved button located in front of the running chronograph totalizer dial.

2.4.2 - The chronograph is operated by two buttons located on each side of the grooved button.

One of the buttons in in charge of, by repeated pressures, starting, stopping and starting again of the time counter (seconds' hand on the large dial and hand of the totalizer).

The other button ensures the reset of the two hands of the time counter when pressed, with persistent notion (hands staying at zero) if the other button previously performed the stop, and with immediate restart if the other button did not previously performed the stop.

2.4.3 - The crown and other controls show no defect.

2.5 - The strap is of good quality, capable to serve for a long time without deterioration.

It is well designed and tough, in no way going off from the bridle and the watch even under repeated traction or friction.

Chapter 3
Operation characteristics

The type 21 chronograph wristwatch can undergo towards its approval process, three series of trials spaced, one from the other, by a time interval that can account to up to 1 month.

During this time interval, the instrument can remain stopped and be subjected to any weather condition present in France.

3.1 - First series of trials

Between the different tests of this series, the instrument can remain stopped for time intervals none of which will exceed 72 hours.

3.1.1 - Test run of 24 hours, in vertical position 6 o'clock up, at +20°C

Daytime rate less or equal to 15 seconds in absolute value.

3.1.2 - Test run of 24 hours, in vertical position 6 o'clock up, in an enclosure at -20°C

No stopping, no incident.

3.1.3 - Test run in any position, in a 12 gauss magnetic field

No stopping, no incident.

3.1.4 - Test run in any position, under an acceleration of 5 g maximum for 1 minute

No stopping, no incident.

3.1.5 - Test run in any position, in an enclosure at 0°C during 5 consecutive cycles of pressure variation consisting each of:

• initial pressure of 1000 g/cm2
• decreasing pressure from 1000 to 300 g/cm2 in 5 minutes
• constant pressure of 300 g/cm2 for 10 minutes
• increasing pressure from 300 to 1000 g/cm2 in 5 minutes
• constant pressure of 1000 g/cm2 for 15 minutes

No stopping, no incident.

3.1.6 - Same test as 3.1.1

Daytime rate less or equal to 15 seconds in absolute value

3.1.7 - During each test 3.1.1 and 3.1.6 and immediately before and immediately after each test 3.1.2 through 3.1.5 we check that all chronograph operations function correctly without incident, and in particular that the transit of the minute on the totalizer is done at most 2 seconds before the top of the minute, without any tallying down whatsoever, not at the beginning not during the operation.

3.2 - Second series of trials

3.2.1 - Quick tests (2 days of trials back to back at +20°C)

Day 1

• at the beginning of day 1, winding
• during day 1, 5 measures of the accuracy of the chronograph, on one hand for 1 minute (highest error P1), on the other hand for 30 minutes (highest error P2)

Day 2

During the first hour of day 2, recording of the

instantaneous rate for 3 minutes, in the 3 following positions:

During the first hour of day 2, recording of the instantaneous rate for 3 minutes, in the 3 following positions:

Position I horizontal, dial up: rate h

Position II vertical, 6 o'clock on the left: rate V1

Position III vertical, 6 o'clock up: rate V2

• Immediately after, 1 measure of the accuracy of the chronograph first for 1 minute (error P1) then for 30 minutes (error P2)
• Immediately after, winding
• During the hour following the winding, recording of the instantaneous rate, for 3 minutes, in positions I, II, III (rates h', V1', V2')
• during day 2, 5 measures of the accuracy of the chronograph, on one hand for 1 minute (highest error P1"), on the other hand for 30 minutes (highest error P2").

Expected results

a = | h' - h | : less or equal to 25 seconds
b = | v1' - v1 | : less or equal to 25 seconds
c = | v2' - v2 | : less or equal to 25 seconds
s = a + b + c : less or equal to 60 seconds
P1, P1' and P1": less or equal to 0.3 second
p2, p2' and p2": less or equal to 0.8 second
No stopping nor incident whatsoever

3.2.2 - Watch setting tests (24 consecutive days of trials)

The instrument undergoes continuous tests in 4 different positions and in 3 enclosures with different temperatures, in conformance with the spreadsheet hereafter:

Days	Position	Enclosure temperature
A	Vertical 6 o'clock up	+20°C
B	Vertical 6 o'clock up	+20°C
C	- d° -	0°C
2 days without winding	- d° -	0°C
D	- d° -	0°C
E	- d° -	0°C
F	- d° -	+20°C
2 days without winding	- d° -	+20°C
G	- d° -	+20°C
H	- d° -	+20°C
I	- d° -	+40°C
2 days without winding	- d° -	+40°C
J	- d° -	+40°C
K	- d° -	+40°C
L	- d° -	+20°C
2 days without winding	- d° -	+20°C
M	- d° -	+20°C
N	Vertical 6 o'clock up	+20°C
O	Horizontal dial down	+20°C
P	Horizontal dial up	+20°C

Expected results

In the spreadsheet hereafter, the letters A, B, C etc. stand for the daily rates in seconds.

Nature of the criterion	Calculation	Expected result
Average daily rate in the different positions	1/4 (M + N + O + P) = ¤	Between -15 and +15
Maximum deviation between 2 consecutive days	A-B;D-E;G-H;J-K	Lower or equal to 12.5 in absolute value
Average positional deviation	1/4 [|M-¤|+|N-¤|+|O-¤|+|P-¤|]	Lower or equal to 12.5
Compensation difference by degree Celsius	((A+B)* - (D+E)) / 80	Lower or equal to 12.5 in absolute value
Daily rate from the days of temperature change	C;F;I;L	Between -30 and +30
Rate correction deviation	M - 1/2 (A+B)	Lower or equal to 21 in absolute value

3.2.3 - Chronograph tests

Once at the beginning and once at the end of each day of setting trial when the instrument is not stopped, due to insufficient winding, we check:

• chronograph accuracy for 1 minute (highest error lower or equal to 0.3 seconds)
• chronograph accuracy for 30 minutes (highest error lower or equal to 0.8 seconds)
• chronograph operation without stopping or incident whatsoever

3.3 - Third series of trials - Tests of use in flight

We check that the instrument is well suited to practical conditions in flight; and in particular, legibility and convenience and toughness of the strap and of the device to attach it to the watch.

Chapter 4
Presentation conditions

Each interested industrialist shall make, before the 31st of May, 1956, offers for prices and delays in order to provide 3 identical prototypes of type 21 chronograph wristwatches.

Offers should be sent in to

Aeronautics technical service
Equipment section

4, avenue de la Porte d'Issy

Paris 15e