The CAS Registry Mumber 670-28-0 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 6,7 and 0 respectively; the second part has 2 digits, 2 and 8 respectively. Calculate Digit Verification of CAS Registry Number 670-28: (5*6)+(4*7)+(3*0)+(2*2)+(1*8)=70 70 % 10 = 0 So 670-28-0 is a valid CAS Registry Number.