Included in this listing:
-Tool to tension the alternator belt (4pk790). This works the same way as shown in the video on the smart fortwo cdi.  For belt 4pk790, the tension for initial assembly should be 450N and 410N for a re-assembly of the belt. With the tool, set the alternator belt tension very precisely to the right tension by turning the wingnut (only with your hands, not with pliers).
-The tool to remove the airco stretchbelt as shown in the video, is not included, as the petrol versions have a tensioner. So you don't need this tool.

Here's a video tutorial on how to replace the alternator belt with the Easy Green Tools. Video shows the fortwo cdi version, but for the petrol version this works just the same. Once again, the removal of the airco belt is different from the video.

http://youtube.com/watch?v=Mu2B6Ql2T6M

The photo of the listing shows the tool on a smart roadster (petrol engine). 

If you don't have special belt tension measuring equipment, you can measure the belt tension with an iPhone or android smartphone. This video shows how.

http://youtube.com/watch?v=KNG9fmwW8vw