AIR uses the chart above to check the rib angles on their gliders prior to shipment. The second section labeled Soll° is the latest angles used for all the Atos gliders (I am not sure about the Atos-S). The angles have changed since the first Atos has shipped. The twist is a little less at the center now. The information filled in by hand was my year 2000 Atos. I installed a new right spar (after a blown launch). You can see that the inboard ribs have more angle than the chart, this is OK, less than the chart is not good. My #8 right rib measured 2.8° on the new spar necessitating a change. After the change it measured 4.7°. The last line Korrektur is the amount of correction in mm needed to make the correct angle. The cart shows 4mm for the right #8 rib. Each 2mm changes the angle about 1°, a little more on the inboard ribs. We moved the top rib pin hole forward 2mm and the bottom pin hole rearward 2mm.
Prior to making any measurements, the glider has to be leveled by the keel (same as the sweep check) and the wings need to be leveled. It is best to hold up the wing from under the spar, holding it at the tip can result in erroneous measurements. Small amounts of wind can also affect the measurements. It is best to do this check on a windless day or indoors.
This is a tool I made to measure the rig angles. I copied the tool used by AIR. Your dealer should be getting these tools to make the proper checks. The angle on the level reads 0.4°. The reason for the two feet on the front of the tool is the front foot is used for ribs #1-#7 and the second foot is used for ribs #8 and #9. The front foot is place over the top of the forward most part of the rib.