The CAS Registry Mumber 690-93-7 includes 6 digits separated into 3 groups by hyphens. The first part of the number,starting from the left, has 3 digits, 6,9 and 0 respectively; the second part has 2 digits, 9 and 3 respectively. Calculate Digit Verification of CAS Registry Number 690-93: (5*6)+(4*9)+(3*0)+(2*9)+(1*3)=87 87 % 10 = 7 So 690-93-7 is a valid CAS Registry Number.