Revision History for SmartSheets?

Hi there.  Revision history and the ability to go back to a previous version from last week or last month is critical when working on a sheet that multiple people update;   in Google Docs revision history shows who changed what field when, in case of problems or disputes this is clearly logged and it is easy to revert to a previous copy if desired.   To be clear, im not referring to the "Undo" button, but to the version history of the smartsheet.   How is this handled on Smartsheets, is there a link or a document showing how to look at the revision history for any given Smartsheet, and if so how far of a history does it keep?   Thanks.