The CAS Registry Mumber 643-83-4 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 6,4 and 3 respectively; the second part has 2 digits, 8 and 3 respectively. Calculate Digit Verification of CAS Registry Number 643-83: (5*6)+(4*4)+(3*3)+(2*8)+(1*3)=74 74 % 10 = 4 So 643-83-4 is a valid CAS Registry Number.