Sure. Most screw systems have springs on both side of the base unit, or along the body of the screw. The extender either use a suction cup or a noose system to hold onto the glans or just below the glans. Each screw system has a marking either on the rod or on the between the cylinders that holds the base of the extender and the device the holds onto the glans or the base of the glans.
If you see the marking on the rods that connects to the screws, or twisting knobs, the marking indicate the traction force in either grams or kilogram. Mostly in grams. What you want to do is use a kitchen scale, assemble together the extender fully, place the base of the extender on the scale, and gently press onto the top of the extender (the attachment to the glans or below the glans), and make a notation on how much weight is needed to compress the rod and cylinders together. This is is your traction force. Each mark, based on the strength of the internal springs, allows you to determine how much traction force is pushed against your penis in an ideal condition. The further the screw being turned to push the penis out (or the traction intensity), the harder the tissues are being placed under pressure for growth.
Hope that helps. If you're still confused, assemble the entire extender together, take a photo, and post it here. We'll help you by doodling the photo to give you more info.