The CAS Registry Mumber 933-42-6 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 9,3 and 3 respectively; the second part has 2 digits, 4 and 2 respectively. Calculate Digit Verification of CAS Registry Number 933-42: (5*9)+(4*3)+(3*3)+(2*4)+(1*2)=76 76 % 10 = 6 So 933-42-6 is a valid CAS Registry Number.