Template:Prev
This template makes a diff link between the specified revision and the previous revision. It takes one parameter, the "oldid" of the revision you want to show. The oldid can be found in the URL in your browser's address bar when viewing diffs or permanent links. When viewing permanent links, the URL will look like this: https://en.wikipedia.org/w/index.php?title=Template:Prev&oldid=639914204. In this case, the value to use would be "639914204". When viewing diffs, the URL will look like this: https://en.wikipedia.org/w/index.php?title=Template:Prev&diff=639914204&oldid=489762261. In this case, you should use the "diff" URL parameter, i.e. "639914204". The "oldid" URL parameter will use the older of the two revisions, which probably isn't what you want.
Syntax
{{prev|oldid}}
Examples
{{prev|639914204}}→ http://en.wikipedia.org/w/index.php?oldid=639914204&diff=prev[{{prev|639914204}} a link]→ a link