Create Chart widget on HABPanel

using version OpenHAB 3
I want to install the Chart widget on my Panel.
add Wigdet Chart to panel -> use item Waterbox
The values from this item are stored in a sql dB.

but the widget shows only zero

HAB_SQL-ChartPanel_values

what type of data is required in version 3 ?

version 2.5 works great:

regards,
Juergen