How does the Dropbox app determine when a file needs to be synced/updated?

[Frank P E.]

Hello --- does anyone  know how  the sync process works?   does it used the date/time/size of the file or the file content to check to see if the file in question has to be synced? 

[Rich]

@Frank P E. wrote:

does anyone  know how  the sync process works?   does it used the date/time/size of the file or the file content to check to see if the file in question has to be synced? 

Content. Date and time don't mean anything.