sir, is it working fine. Please, tell sir

sir, please tell why they do bitwise and operation with 0x00FF while calculating checksum. Please do explain..

sir, do you have the documentation for A01NYUB  sensor. Please, tell sir. what is the difference between processed value vs real time value. 

Bro is this sensor working for you. do you know what is the significance of 

SUM=(Header+Data_H+Data_L)&0x00FF
=(0XFF + 0X07 + 0XA1)&0x00FF
=0XA7;

0x00FF here. please tell