Help Slow Down GB Disc Pendulum Clock

Hi
Could you all please help me slow down the Gustav Becker disc pendulum clock that was my dad's? I see the S/F knob but don't know how to adjust it.
Your help is greatly appreciated!
Pattye

Pattye,
There should be a square on one end of the rod that goes through the two small weights and a couple of arrows on one of the weights to indicate which way to turn the rod to move the weights toward or away from each other. This should speed up or slow down the clock, depending on which way you turn the rod. My clock shows that turning the rod clockwise will slow the time. Be VERY careful when turning the rod; it has a notch in the center where it passes through the body of the pendulum disc and is very easy to twist in two. A watch key or the small end of a carriage clock key will fit the square on the rod. It may need a thinner suspension spring than the one currently in use.

The calibration weights in the picture you posted look to be adjusted as far as they go for "slowness".
To make it run slower yet means a little more weight needed in the pendulum or a lighter suspension spring. I had a similar problem and unhooked the pendulum, and as the clock is VERY OLD, I opted to increase the pendulum weight.

I disconnected the pendulum hook from the suspension, and unscrewed the nut holding on the bottom cover. Inside the pendulum "cup", I added some thin "lead string" weight I got at a fishing store. It takes some fiddling around, but it worked. Also during that "operation", I was able to return the adjustable weights a little closer to the middle of their "range" to allow for any later recalibration. If that makes you nervous, I recommend you unhook the pendulum, and take or send the whole clock and pendulum to a clocksmith.

Thanks so much for your replies. The problem is--the clock just returned home from the clockmaker who told me to adjust the weights with a small key but now I am afraid to try. The clock is gaining about 2 minutes a day and I had hoped to adjust it more accurately but now I am afraid to cause permanent damage and will probably leave well enough alone. The clock made a 600 mile trip from the clockmaker and I don't want to repeat that!
Pattye

Pattye, Two minutes a day for a 400 day clock means stay away from adjusting it, as it is adjusted very well. Keep it out of the sun, and every day or so reset it. You may be pleasantly surprised that it will "settle down" to less than that error after a few weeks. Also you will find that it can sometimes run faster and slower with the seasons, birthdays, rainy days, and different phases of the moon!

David:
So-what we have here is a not-so-accurate finicky clock. I will learn to live with it. Thanks for your help.
Pattye