Hi luuk,
Let me try to help. I bumped your trust level. Try again, if you can upload the file.
Until then here some tips 
:
- If you want to use time series graphs use the x/y chart.
- check out this post to create a good source range for your chart: How to save incoming messages in a history!
- Also this post could be useful: Adding chart to track value over time fails
Cheers,
Tizian