Time Machine
Time Machine allows you to view all the past iterations of a sales order or purchase order. It's possible to 'rewind' the history of the document and see all the changes that have been made, together with the users who made the changes and the dates and times the changes were carried out..
It is accessed from the [ Sales Order | Main ] screen or the [ Purchase Order | Main ] screen by clicking on the rewind button 
on the Button Bar, after loading the sales or purchase order whose history you wish to view.
This will open the History dialog:
By dragging the blue slider along the bottom of the dialog box, the loaded document will change to show the state it was in at various points in time along the scale. At the point of each change, the dialog will show the user who carried out the change, and the date and time it was done.