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The UV set needs to be of type VDB Float because we are dealing with a VDB file, and the grid that's creating the UVs (the temperature grid in our case) is of type float. The reason we chose the "00" is because this is the first float grid that we are using. If we had two float grids that were generating UVs (both where specified in the "Additional grids for UV" parameter), and we wanted to use the second one, we would instead have chosen VDB_FLOAT_01. If there where 3 float grids specified and we wanted to use the third one, we would have chosen VDB_FLOAT_02 and so on. Please keep in mind that the count starts at 00, not 01.
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To accurately map the entire range of the gradient to the temperature UVs, we need to know the range of values found in the temperature grid. To do this, make sure "temperature" is written in the Additional grids for UV parameter and launch a render. In the Console panel, the values for this grid will now appear:
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