The CAS Registry Mumber 423-03-0 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 4,2 and 3 respectively; the second part has 2 digits, 0 and 3 respectively. Calculate Digit Verification of CAS Registry Number 423-03: (5*4)+(4*2)+(3*3)+(2*0)+(1*3)=40 40 % 10 = 0 So 423-03-0 is a valid CAS Registry Number.