Center of Gravity

Properly trimming an aircraft is critical to getting the most out of a your sailplane.
What you are looking for is the sweet spot where your sailplane will fly at its best.
It takes a lot of time or days to accomplish this task of trimming or making minor adjustments .Trimming your plane is a continuous process.

Center of Gravity is the difference in position between the Center of Gravity and Center of Lift on a plane. If the static margin is forward of the center of lift. The plane will continue to fall forward in the air and keep flying. Conversely, if the center of gravity is behind the center of lift with a negative static margin, the plane will be unstable, and the plane will stall constantly. Where should I set up the zero static margin of my sail plane. If the CG is to far forward you will add more up elevator and create more drag. when this is present you can fly through a thermal and not know that one was there hurting the performance of the sailplane. Every pilot will have a different feel with their sailplane in different conditions of what the day is giving them, so setting the CG is largely a matter of personal preference.
The manufacturer's recommended position is usually the center of the spar, and represents a good safe bet for the first few days of flying.
When you are setting up a new plane it is a good though to do this on a day that is not to turbulent.

Dive Test Your Sailplane

Trim your sailplane for normal speed, level flight. Next, put the plane in a shallow dive approximately 10 to 15 degrees then take your hands off the sticks. If the plane very gently pulls out of the dive, it is properly trimmed. If it pulls out rather sharply, it is nose heavy, remove some weight. If the plane tucks under or sharpens the dive, additional nose weight is needed. Repeat the test until a very gentle dive recovery is observed. Recommenced to add or subtract about 1/4 oz at a time. This is a great starting point to set the static margin of the CG over the CL.