The CAS Registry Mumber 1231-03-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,2,3 and 1 respectively; the second part has 2 digits, 0 and 3 respectively. Calculate Digit Verification of CAS Registry Number 1231-03: (6*1)+(5*2)+(4*3)+(3*1)+(2*0)+(1*3)=34 34 % 10 = 4 So 1231-03-4 is a valid CAS Registry Number.