The CAS Registry Mumber 1988-09-6 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,9,8 and 8 respectively; the second part has 2 digits, 0 and 9 respectively. Calculate Digit Verification of CAS Registry Number 1988-09: (6*1)+(5*9)+(4*8)+(3*8)+(2*0)+(1*9)=116 116 % 10 = 6 So 1988-09-6 is a valid CAS Registry Number.