The CAS Registry Mumber 810-43-5 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 8,1 and 0 respectively; the second part has 2 digits, 4 and 3 respectively. Calculate Digit Verification of CAS Registry Number 810-43: (5*8)+(4*1)+(3*0)+(2*4)+(1*3)=55 55 % 10 = 5 So 810-43-5 is a valid CAS Registry Number.