Thursday, February 03, 2005

Understanding a JLC Master Control Test Report Printout

One of the best bits of the Master Control Test report is the following printout:

Column 1: Position.

VB = Vertical Bas (Crown Down)
VG = Vertical Gauche (Crown Left)
VH = Vertical Haut (Crown Up)
VD = Vertical Droit (Crown Right)
HH = Horizontal Haut (Dial Up)
HB = Horizontal Bas (Dial Down)

An ideal case is where a watch runs at the same rate irrespective of force feeding the escapement i.e. the power in the spring. So the testing in the 6 positions is carried out fully wound (0 h) and after 24 hours (24 h) .

Columns 2 and 3: Daily rate: The corresponding rates for each position you can see in columns 2 (0 h) and 3 (24 h).

Column 4: Difference in daily rate. Simply the difference between columns 2 and 3 (a low number would be good).

Columns 5 and 6: Beat Error. This is the number of milliseconds difference between the length of a tick and a tock. It's just a check of whether the watch is "in beat", i.e. with the balance wheel unfed with power, does it naturally rest in the middle of its swing? Column 5 (0 h) and column 6 (24 h)

Column 7 and 8: Balance Wheel Amplitude. You can clearly see the lower amplitude in the cases after 24 hours running (numbers like 267 deg dropping to 228 deg for example).

Delta: The maximum difference across any of the positions (in this example -1 to +3 gives a delta of 4 at 0h and +4 to -3 gives a delta of 7 at 24 h.

Val. m: is the average accuracy of the watch in every position rounded to one significant figure. It is the sums of column 2 and then column 3 respectively divided by 6.

Isochron max: The maximum difference in rate shown between 0 h and 24 h running in any of the positions.

"Qualit├Ąt N. = 2.5" is a result generated by the machine which is not used by JLC.


Anonymous said...

Thanks for your explanation of a JLC Master Control report and the sample report you posted. Can you interpret the sample report...was the watch that was tested for the sample report a very accurate watch, average, or a not very accurate watch?

Richard M

Velociphile said...


I honestly don't know, I've only ever seen four MC reports; another similar to this and a couple slightly poorer. May be best to post a question at the forum, but I think it's splitting hairs to categorise them.

All JLCs seem to leave the factory inside the COSC "-1 to +6" spec as, anecdotally, most JLC owners seem to report something like 0 to +2 or 3s per day. Especially if kept fully wound on the wrist. That is also my own experience.