The CAS Registry Mumber 673-54-1 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 6,7 and 3 respectively; the second part has 2 digits, 5 and 4 respectively. Calculate Digit Verification of CAS Registry Number 673-54: (5*6)+(4*7)+(3*3)+(2*5)+(1*4)=81 81 % 10 = 1 So 673-54-1 is a valid CAS Registry Number.