The reason I got into watch repair to begin with is because I hate spending a ton of money on anything that I think should be cheap or easy. I feel the same way about watch timers. Perhaps, once I graduate beyond the basics I will invest in a proper watch timer. But for now I just wanted a quick way to tell if a watch is running at the correct rate. I attempted too use my PC to time the watch...and it failed. I explain below. But through trial and error I was able to get it back to running on time. 

Why not Use Your Computer to Get it Close?
I thought that using nothing more than a Laptop and free audio software I could regulate a watch. Granted, this method wouldn’t allow you to find error in the escapement and such. But to get a general idea of the rate at which a watch is running it would work...right???

Here's What I Did...
Step 1: Downloaded a free audio recorder. I like Free Audio Editor 2015 from download.com. 
Step 2: Went into a quiet place and set the watch to be recorded on the microphone. You can use any microphone for this, you will find it easier to get one that plugs in, but I hang the watch over the top of the Laptop screen so that it rests on the built in microphone. 
Step 3: Recorded about 65 seconds of the watch ticking. You will see the ticks as sharp peaks if everything is set right. 
Step 4: Trimmed the recording to a 60 second clip. When I trim the recording I start just after a peak and highlight until the length of the clip equals as close to 60 seconds as I can get. 
Step 5: Counted the peaks. With a 60 second clip there should be 300 peaks, these represent the ticks and tocks of the watch. If you have 300 then you know that the watch is running accurately. This is because a 18,000 bph movement has 300 beats per minute (18,000/60). 
Step 6: Error rate. Let say you don't get 300 ticks, let say you get 301 ticks on the graph. "Not Bad..." you think...

Wrong! What is that error rate? To find the error rate simply divide the ticks by the number of seconds. For our example we had 301 beats in 60 seconds. 301/60 = 5.0166 beats per second. The watch should be running at 5 beats per second. That means the watch is gaining 0.017 beats per second, or 0.017 * 60 seconds = 1.02 beats gained per minute, or 61.2 beats per hour. That is 12 seconds an hour. That is about 5 minutes a day... In order to be effective you would need to record about 10 minutes and count all the ticks...3,000 that is, to look for one extra...even that would still be a 1 second per hour error rate. 

The Better Way: Trial and Error
​Step 1:  Log into the Time.gov website. This is the official government website for the current time. What is nice is it gives time in seconds. Check the watch, note how many seconds fast or slow it is at that moment. I wear the watch during this process so it is moving around.
Step 2: Check again in 2 hours, make a note. 
Step 3: Check again in 2 hours, and adjust the regulator. 
Step 4: Check again in 2 hours, and adjust the regulator more. You may go too far and then have to come back. Eventually it will balance out and you will find the sweet spot where it runs most accurately. TINY ADJUSTMENTS are all that is needed. 
Step 5: Once it runs 2 hours accurately, move to every 4 hours and Check and Adjust.
Step 6: Then Check and Adjust every 6 hours. 

I try to regulate the watch to be within 2 - 10 seconds a day (depending on the watch). I have heard people say under a minture a day is fine for vintage watches. Two seconds or less a day that would keep you under 1 min a month, and 10 seconds at the max is about 5 minutes a month. I usually don't wear the same watch for more than a day or two, so long term accuracy is not as important.

UPDATE: To make it a little simpler if you are running for 4 hours and gain/lose less than 1.5 seconds you are good to go.  One minute a week is great for a vintage watch. That is 8 - 9 seconds a day. Break that down further and you have about 1.5 seconds in four hours. 

Below is the Swiss Chronometer standard for modern mechanical watches. As you can see a high quality modern watch is allowed -4 to 6 seconds per day variation (that is a 10 second swing). Six seconds a day is 42 seconds a week, just under a minute. 

COSC Chronometer Certification parameters:            Average daily rate: -4/+6 seconds / day
            Mean variation in rates: 2 seconds / day
            Greatest variation in rates: 5 seconds / day
            Difference between rates in Horizontal & Vertical positions: -6/+8 seconds / day
            Largest variation in rates: 10 seconds / day
            Thermal variation: ±0.6
            Rate resumption: ±5 seconds /day


Good Luck!

Recently I purchased a 1940's Invicta tank style watch. It was an impulse buy and for under $10 I figured I could make a buck on the deal. It needed work. It was not running, missing a crystal, and had no sub-second hand. Tried as I might I could not locate a reasonably priced crystal for it. Luckly, I have a shoe box of old watch crystals purchased a while ago of various size all vintage glass. I dug through that box and found one that was close. It at least had the same general shape. And it was only about 3mm too large.

I got my hands on a set of diamond hones from Harbor Freight ($10) and went to task grinding down the crystal. It took an hour or two and I went slow and wet the stone to avoid excessive heat and chipping. The end result is not too bad. A watch looks much better with a crystal than without. 

Try it!