If you can read it some place, we can graph it.
Example with a cli command you can get the needed value, you can send it out from your router using Syslog.
Then this data can be used in Splunk to make nice graphs.
Look here for some user of it:
http://forum.mikrotik.com/t/tool-using-splunk-to-analyse-mikrotik-logs-3-3-graphing-everything/121810/1