Those lines are ml measurements for doing dilutions with the DPD test. They must use the same comparator mold for all the 2000 series comparators so those lines are probably on all of them. With the DPD test (not the FAS-DPD test you can fill the comparator to the 4.5 ml line with pool water and then to the 9 ml line with distilled water for a 1 to 1 dilution which means the DPD test results are doubled. By using the 1.8 ml line and then filling to the 9 ml lline with distilled water the DPD test results ar multiplied by 5 to give an estimation of chlorine levels up to 25 ppm but with limited precision.

The CYA scale is the ppm scale on the front that goes from 30 to 100 ppm (or the molded scale on the OTHER side (the inside, not the outside) that goes from 30 to 100 ppm if you have a K-2005 comparator.)

Since you are lining up at the 1.8 ml mark you CYA is off scale. The 4.5 ml mark is about80 ppm CYA so your is MUCH higher. You are going to have to do the dilutions as BigDave suggested.