In the case where a shareholder with 100 shares transfers 20 to another shareholder, split the shares by transferring them from the existing certificate to two new certificates, i.e., allocate 80 shares to the old shareholder with a new share certificate number. Then allocate 20 shares to the new shareholder.
E.g., Shareholder A transfers 20% of his holdings to Shareholder B
Cert No. 1 A____100%____
Transfer as follows:-
B Cert no.2 __20%____
A Cert no.3 __80%____
However if you are doing the split it is only necessary to do the first part i.e. the 20%, and then the system will ask you if you want to generate the balance certificate. If you say Yes the 80% will be generated automatically to a new share certificate number.