The CAS Registry Mumber 1308-09-4 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,3,0 and 8 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 1308-09: (6*1)+(5*3)+(4*0)+(3*8)+(2*0)+(1*9)=54 54 % 10 = 4 So 1308-09-4 is a valid CAS Registry Number.