As a little exercise I have been tracking the accuracy of several of my watches, 4 TC, a precisionist and a standard quartz that looked to be keeping fairly good time. I have not been concerned about temperature as a variable and realize that this could impact my results significantly. What I was more looking for was to see how well the various watches were keeping accuracy over time, as they are part of a larger collection that gets worn on the basis of a watch change every 1 - 3 days depending on mood and needs. As I also have several AT watches that are part of the wrist rotation it means that any given watch could conceivably not see wrist time for a couple of weeks (or longer for lesser favourites).
The watches in the test were:
- Breitling Airwolf Raven
- Bulova Precisionist Claremont
- Maurice Lacroix Miros Diver
- Seiko Worldtime Flightmaster SNJ017
- Sinn UX
I also am testing the Christopher Ward C70 Brooklands COSC, but currently have too few data points to use for the chart.
My methodology was to check the watches by the stopwatch method using my Citizen Skyhawk AT (after making sure that it had made a successful sync within the last day). At the start of the test I set all the watches and then took an initial reading to account for the small setting inaccuracy (the worst was off by ⅓ of a second based on my pathetic reaction times). At each test point I took 5 readings (sometimes more if one reading was significantly different from the others, replacing that reading). The readings were based on a 15 second comparison period, starting the reading as the second hand passed a certain marker on the "checked" watch, and taking the stopwatch reading on the AT watch as it's second hand hit the same marker plus 15 seconds. I took the average and then computed an expected SPY value based on the following formula:
SPY (est) = (Reading - 15 - original offset ) * 365 / (test date - start date)
I tabulated the values for each of the 5 watches, and while seeing relatively as expected performance from most of the watches I was noticing that for some there seemed to be an increase in the projected SPY as time progressed. It was at this point that I decided to create a plot of the SPY versus days (test date minus start date), and then use Excel's trend line tool to project out to 365 days. This captures an "acceleration" effect. The chart below shows the results:
The Breitling and Sinn show relatively flat curves (lines) projecting to -2.76 spy (versus an average estimate right now of -7 spy) for the Breitling and 16.76 spy (versus an average estimate right now of 12.5 spy) for the Sinn. Both fall within COSC (at 25.5 spy), and the current average values are quite acceptable to me. The Sinn will get corrected at the fall and spring time changes, but the Airwolf will go the full 365 days on the test, as time change can be achieved without touching the minutes/seconds.
The Seiko is not providing any real surprise, and even projected out to 365 days is showing about 82 spy, which is better than the monthly range of +/- 15 spm would project to at an annual rate (180 spy).
The Precisionist is not looking anywhere near as good as the advertised claims, but then too is getting very little wrist time. I am sure that its numbers would be better if worn daily, but based on comments I have heard from a number of sources the 10 spy number is suspect.
The real shocker is the Maurice Lacroix Miros Diver (ETA 251.232). While early numbers were projecting a quite low spy, the last three checks were giving 13, 15 and 18 spy. This projects out to a very un COSC, un TC, 64 spy at 365 days! I will continue to monitor this situation, and will contact ML.
I am 121 days into my test and will continue monitoring until 365 days have passed (the Sinn and Precisionist will end the test at the fall time change as their seconds/minutes hands are affected when changing the time). The other 3 can adjust the hour hand independently.
The watches in the test were:
- Breitling Airwolf Raven
- Bulova Precisionist Claremont
- Maurice Lacroix Miros Diver
- Seiko Worldtime Flightmaster SNJ017
- Sinn UX
I also am testing the Christopher Ward C70 Brooklands COSC, but currently have too few data points to use for the chart.
My methodology was to check the watches by the stopwatch method using my Citizen Skyhawk AT (after making sure that it had made a successful sync within the last day). At the start of the test I set all the watches and then took an initial reading to account for the small setting inaccuracy (the worst was off by ⅓ of a second based on my pathetic reaction times). At each test point I took 5 readings (sometimes more if one reading was significantly different from the others, replacing that reading). The readings were based on a 15 second comparison period, starting the reading as the second hand passed a certain marker on the "checked" watch, and taking the stopwatch reading on the AT watch as it's second hand hit the same marker plus 15 seconds. I took the average and then computed an expected SPY value based on the following formula:
SPY (est) = (Reading - 15 - original offset ) * 365 / (test date - start date)
I tabulated the values for each of the 5 watches, and while seeing relatively as expected performance from most of the watches I was noticing that for some there seemed to be an increase in the projected SPY as time progressed. It was at this point that I decided to create a plot of the SPY versus days (test date minus start date), and then use Excel's trend line tool to project out to 365 days. This captures an "acceleration" effect. The chart below shows the results:
The Breitling and Sinn show relatively flat curves (lines) projecting to -2.76 spy (versus an average estimate right now of -7 spy) for the Breitling and 16.76 spy (versus an average estimate right now of 12.5 spy) for the Sinn. Both fall within COSC (at 25.5 spy), and the current average values are quite acceptable to me. The Sinn will get corrected at the fall and spring time changes, but the Airwolf will go the full 365 days on the test, as time change can be achieved without touching the minutes/seconds.
The Seiko is not providing any real surprise, and even projected out to 365 days is showing about 82 spy, which is better than the monthly range of +/- 15 spm would project to at an annual rate (180 spy).
The Precisionist is not looking anywhere near as good as the advertised claims, but then too is getting very little wrist time. I am sure that its numbers would be better if worn daily, but based on comments I have heard from a number of sources the 10 spy number is suspect.
The real shocker is the Maurice Lacroix Miros Diver (ETA 251.232). While early numbers were projecting a quite low spy, the last three checks were giving 13, 15 and 18 spy. This projects out to a very un COSC, un TC, 64 spy at 365 days! I will continue to monitor this situation, and will contact ML.
I am 121 days into my test and will continue monitoring until 365 days have passed (the Sinn and Precisionist will end the test at the fall time change as their seconds/minutes hands are affected when changing the time). The other 3 can adjust the hour hand independently.