The CAS Registry Mumber 688-44-8 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 6,8 and 8 respectively; the second part has 2 digits, 4 and 4 respectively. Calculate Digit Verification of CAS Registry Number 688-44: (5*6)+(4*8)+(3*8)+(2*4)+(1*4)=98 98 % 10 = 8 So 688-44-8 is a valid CAS Registry Number.