Does -u update override -c checksum only?

Maybe I’m misunderstanding these two options. I want to copy files only when the checksum is different AND the source file modification datetime is more recent (if the file exists). I’m doing some testing and it looks like if you use the -u update option it transfers the file if the source is newer regardless if the checksums are identical. Is this right or am I misunderstanding the options and/or how the checksum is calculated? I thought the checksum was done on the contents of the file, or does it also include the modification datetime in the calc and that’s why it is still transferring?

The -u option does override -c so if the mod times are more recent it will be transferred.

Maybe we can think of a different way… What are you trying to achieve?