Tools & Background
After initially posting this page, a number of watchmakers commented on that I am missing a few tools. To do this procedure absolutely correctly requires a pressure tester so that the cased movement is as waterproof as it was prior to opening , and secondly, a timing tool to measure beat rate, poise, and amplitude. Amplitude (the amount the balance swings in each direction) is important as this will tell you how much variance there is going to be when the watch is face up, face down, and in various other positions. In this .wmv clip on overhauling a 1570 movement, you will see the use of a timing tool. Without a timing tool, you are timing in the dark. Nevertheless, for a simple adjustment, a timing tool is not required, but just be prepared for some guess work. (click for larger image).
A great manual describing how to use a timing machine and all the variables involved is posted here.
The tools required are similar to the tools reqired for removing a Rolex caseback. In addition to the caseback removal tools there are also a Microstella wrench, and a Dumont #7 pair of watchmakers tweezers required for this procedure. The Dumont #7 tweezers differ than the norm because the point curves. These tweezers are used to hold the balance wheel while the Microstella wrench turns the screws. These tools are available from Otto Frei, Jules & Borel, as well as other watch supply houses.
The Microstella screws are designed such that if the screw comes inward, the balance speeds-up, similar to an ice-skater doing a spin; skaters bring their leg in to speed up. The screw going outward will slow the balance down.
An adjustment on a small screw = 1 second/day and an adjustment on a large screw = 2 seconds/day
Any adjustment on one screw requires the same adjustment on the opposing screw or else the balance will be adjusted out of poise.
(click image for larger picture)
(click scans for larger size) Scans from Tony Axelzon, used with permission.
To determine how much to turn the screw, the wrench has an index marked by a freely moving balanced indicator inside the wrench. This vintage image illustrates the wrong way to hold the wrench and the balance. The tweezers are not supported and can easily break the balance staff.
This image from the Rolex Factory Service brochure that is included in the latest Rolex packaging shows more than what Rolex does to regulate a watch; it shows how to hold the tweezers to keep the balance steady. This watchmaker is using the balance bridge to steady the tweezers. Use the balance bridge to guide the tweezer tongs onto the balance wheel.
(click for larger image)
Okay... The Steps
Before removing the caseback (steps here), first detemine how much ajdustment watch requires and calculate whether one has to adjust the larger screws (two-seconds a notch in the Microstella wrench) or the smaller screws (one-second a notch). Then, secondly, determine whether you have to turn the screws inward to speed up the balance, or outward towards the rim of the balance wheel to slow down the balance.
Turning the screws clockwise = screws going inward = speed up
Turning the screws counter-clockwise = screws going outward = slow down
Practice using the Microstella wrench and determine how far and in what direction you need to turn the screws before actually adjusting the balance, similar to how a golfer does practice swings before going to the tee.
Unscrew the winding crown, and pull it out all the way such that the second hand, and the balance stops.
Be sure to notice the two divet locations (red arrow above) for you to discern the opposite Microstella screw. Sometimes the balance wheel will slip free and spring back-and-forth, losing your reference on which Microstella nut you were adjusting.
Be sure not to touch the hairspring. There is plenty of room beween the balance and hairspring, but do not be fully caffienated with coffee when doing this procedure. Additionally, be sure to be using a loupe so you can see the wrench being slipped onto the Microstella screw.
(click for larger image)
Steady the balance by using tweezers before turning the screw. Use the balance bridge to steady the tweezers as noted by the blue arrow. Then carefully slide the Microstella wrench onto the nut (black arrow) and turn the screw the direction required. When doing this, look at the amount that the screw is being turned as practiced with the golf swings above. Do not look at the wrench indicator as you want to keep everything steady.
When the first nut is adjusted, then gently rotate the balance to the opposite side of the balance and repeat the same steps. The balance will move slowly as it is being braked. remember the location of the divets in the balance wheel spoke (red arrow) which will help you remember which nut you adjusted. There are only two of these divets marked on the balance wheel.
Once completed, depress the crown so that the balance runs freely and replace the caseback. Do not fully tighten the caseback as there will probably be some further adjustments after placing the watch on the timing machine (mentioned below). It took me three tries before I found the correct combination. After replacing the caseback, wear the watch for a full 24 hours before determining whether more adjustment is necessary and before fully closing the caseback.
After adjusting my watch, there is a definite feeling of accomplishment. Akin to open heart surgery, this procedure does take a steady hand and the proper tools, but it is possible for watch owners to regulate their own Rolexes. The procedure was easier than picking any of the parts in the Operation game. If you can play this game without the buzzer going off, you certainly can turn Microstella screws in a Rolex.
Update: I purchased a TYMC timing machine from Orbita and it is a great little device. Below is an image of my GMT 116710 on the machine. By the looks of it, no regulation is required.
This is the screen with the 116710 face up. The S/d is standard deviation / Day. The 308 degrees is amplitude, and the beat error is .1ms, very well within specification.