The Transmission Gui has a counter in the bottom right that will tell you:
- Total Ratio
- Session Ratio
- Total Transfer
- Session Transfer
The Session Ratio and Transfer is what you would expect.. The amount since you last started up Transmission.
The Total Ratio and Transfer is from the start of time using Transmission or since you last cleared the stats.
You can clear the stats by deleting the stats.json file located in ~/.config/transmission/stats.json
Its handy to clear this the start of every month or setup a cron to do this for you. I find it just lets me keep my downloading a little more under control.