The CAS Registry Mumber 7697-33-8 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 7,6,9 and 7 respectively; the second part has 2 digits, 3 and 3 respectively. Calculate Digit Verification of CAS Registry Number 7697-33: (6*7)+(5*6)+(4*9)+(3*7)+(2*3)+(1*3)=138 138 % 10 = 8 So 7697-33-8 is a valid CAS Registry Number.