The CAS Registry Mumber 680-63-7 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 6,8 and 0 respectively; the second part has 2 digits, 6 and 3 respectively. Calculate Digit Verification of CAS Registry Number 680-63: (5*6)+(4*8)+(3*0)+(2*6)+(1*3)=77 77 % 10 = 7 So 680-63-7 is a valid CAS Registry Number.