The CAS Registry Mumber 620-03-1 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 6,2 and 0 respectively; the second part has 2 digits, 0 and 3 respectively. Calculate Digit Verification of CAS Registry Number 620-03: (5*6)+(4*2)+(3*0)+(2*0)+(1*3)=41 41 % 10 = 1 So 620-03-1 is a valid CAS Registry Number.