Why we should call Factories act 1948 as " 63 of 1948" and its amendment as "20 of 1987"

Dear sir,
Why we should call Factories act 1948 as " 63 of 1948" and its amendment as "20 of 1987"
What is meant by these act no "63" and "20"
Please explain

Dear Bhaskar,
The no before " of " refers to the serial no of legislation by the Parliament Uand the no after it refers to the year of legislation.

The numbers 63 & 20 denote the chronological order in which the legislature has passed the respective act and thereafter the year of passing the Act is referred. The Factories Act 1948 having been passed by the Parliament received the assent of President of India on 23rd September 1948 and came into force on 1st April 1949.