The CAS Registry Mumber 1643-10-3 includes 7 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 4 digits, 1,6,4 and 3 respectively; the second part has 2 digits, 1 and 0 respectively. Calculate Digit Verification of CAS Registry Number 1643-10: (6*1)+(5*6)+(4*4)+(3*3)+(2*1)+(1*0)=63 63 % 10 = 3 So 1643-10-3 is a valid CAS Registry Number.