A few different elements are seen on the dial, all worth highlighting.
Colorful circles
What makes the Mido ref 5907 stand out in a crowd is the colorful dial, design to prevent confusion during dives, with each concentric circle representing the decompression period necessary.
Each of the four different depth circles begin with “0” and increase as you read clockwise within the circle. The amount of time from 12 o’clock to the “0” is the “clean time”, which is the time not requiring decompression. The numerals following the “0” on the circle indicate the decompression period required in relation to the time spent under water and the depth reached.
Okay, so I’m diving, how do I read this #$@!& dial?!
As an example, on a METRES/METERS dial, the outer blue ring reads “40” at 12 o’clock, which indicates that circle should be used for depths from 40 to 45 metres (depths beyond 45 metres are not shown due to the danger of divers’ narcosis). The “0” appears opposite the 10 minute mark, indicating you can stay at 40-45 metres for 10 minutes without requiring decompression. If you stay for 25 minutes, you would look opposite the 25 minute mark and read 30 within the blue circle, indicating you require 30 minutes of decompression.
Interesting, we can see the change in decompression tables from early white dials to later black dials (see below), specifically a change to the most shallow and deepest depth shown on the dial.
Let’s use the metres dial for an example. With the early white dial (top left, below), if you were at a depth of 40 metres for 55 minutes (outer blue ring), you would require 80 minutes of decompression. Using the later black dial (top right, below), at the same depth and time we see a new dive table is used, advising a more conservative 90 minutes.
Similarly we can see the dive tables change for diving at 25 metres (center yellow ring), again comparing top row images below. At 25 metres the earlier dial shows diving for approximately 34 minutes without requiring decompression, whereas the later dial indicates you can dive to 30 minutes without decompression.
For dive times in the middle of the range shown on the dial (30-35 metres), we also see decompression recommended starting slightly earlier in the dive.
Outer dial color
The outer edge of the dial, beyond the blue ring, will be either black or white in color.
Other than that space, dial colors be the same for all watches – the colored decompression timing rings, the white center circle, and black background color where depths are shown at 12 o’clock. I should say that is the case for…most all watches. I have seen images of one watch with depths on a white background, shown below. This dial has much lighter rings, which appear faded, though so consistent in fade that I would be interested in seeing in person, and utilizes a different dive table than those used on pieces noted above. This watch can be most easily identified by the 75 minute decompression time on the outer blue ring at 55 minutes. This interesting watch is an early serial (2210569), which presumably accounts for the use of a different dive table. We see a more conservative dive table used for watches with lower serial numbers, as well as later serials, before the shift again to a still more conservative table.
Units of measurement
At the top of each dial on either side of the index mark at 12 o’clock is text for the unit of measurement, reading either METRES – METERS or FEET – FEET.
Overall we see more dials with metres/meters as the unit of measurement versus feet.
Numerals within inner circle
Inside the center concentric circle are numerals 3, 6, 9 and 12, with the applied ‘Mido’ emblem just below the 12. The applied Mido emblem appears to be silver on black dials and gold on white dials, though on a number of the images found it is quite difficult to be certain of the color.
Depending on the watch, the hour numerals may or may not be luminous, and there may or may not be plots indicating hours other than 3, 6, 9 and 12. There are no hard and fast rules on when numerals are luminous (though it is uncommon on white dials) and when there are plots (uncommon on black dials).
Text at 6 o’clock
Mido 5907s in the 221x and 310x ranges will have SWISS MADE text at 6 o’clock, with SWISS to the left of the 6 marker, and MADE to the right. In the 252x range we expect to see T SWISS MADE T. We see this text consistently on both black and white dials.