The CAS Registry Mumber 6908-55-0 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 6,9,0 and 8 respectively; the second part has 2 digits, 5 and 5 respectively. Calculate Digit Verification of CAS Registry Number 6908-55: (6*6)+(5*9)+(4*0)+(3*8)+(2*5)+(1*5)=120 120 % 10 = 0 So 6908-55-0 is a valid CAS Registry Number.