Please help with ospf cisco command..i need to understand why the ID process is different?

I did the show ip ospf commad on a device and the ID process was 45...that was the only ID....a few hours later i used the same command and the ID process was 48 for the same device...why? does the ID change automatically or someone change manually? I am confused...that was the only ID 45 and then change to 48...does it change automatically?