The CAS Registry Mumber 2685-24-7 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 2,6,8 and 5 respectively; the second part has 2 digits, 2 and 4 respectively. Calculate Digit Verification of CAS Registry Number 2685-24: (6*2)+(5*6)+(4*8)+(3*5)+(2*2)+(1*4)=97 97 % 10 = 7 So 2685-24-7 is a valid CAS Registry Number.