Water Level Sensor converter (From Arduino to Raspberry )

Hi, we have a problem with converter the data acquired from a water level sensor,
The work is:
Water level Sensor send data to arduino uno ( the unity of water is "ml" ) and then through i2c the arduino uno send data to rasberry pi 3; in the end with node red we were able to receive data and see it through the Dashboard, but the unity of data is "unit" and not "ml".
THIS OUR CODE AND IMAGE.
image

IMAGE OF DASHBOARD :
image

You can set the units in the ui-gauge nodes settings.