The CAS Registry Mumber 66108-04-1 includes 8 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 5 digits, 6,6,1,0 and 8 respectively; the second part has 2 digits, 0 and 4 respectively. Calculate Digit Verification of CAS Registry Number 66108-04: (7*6)+(6*6)+(5*1)+(4*0)+(3*8)+(2*0)+(1*4)=111 111 % 10 = 1 So 66108-04-1 is a valid CAS Registry Number.