We choose to use the Constant Force Balance system because of their simplicity - they work well forever. The Constant Force Balance has no moving parts! It consists of a 1/2" wide stainless steel band that is formed into a coil with a specific tension. We make up assembly to precisely match the weight of the sash. The of the Constant Force Balance is mortised into the sash just below the meeting rail and it's "tongue" is fastened to the bottom of the sash. This hangs the sash with perfect balance. The result being that the sash will stay where you put it. Whether you raise it 2" or 20" it will stay put.
The plastic housing in the picture to the left is mounted into a mortise in the jamb, just below the bottom meeting rail. The "tongues" protruding from the housing are fastened into the bottom of the sash through the holes visible in the picture. This essentially creates a saddle onto which the sash can sit. Once that is accomplished the sash is then "hanging" by the calibrated coil springs. Trouble-free simplicity.