paraview - plotting difference to reference data
 

I am using paraview 3.6.2. I compute time-dependent velocity data,
but these vary more rapidly in space than in time. Therefore,
I want to plot the difference to a reference state in order to visualise the
timedependent variation.

I do not want to write out the differences as well as the data
because this increases the amount of data a lot, I want to save just
the timedependent data and the referencde state.

How can I visualise the difference between the set of timedependent data v1,v2,...
and the single reference state vRef?
I have used the calculator to assign differrent names to the v-fields,
then I used "group datasets" to join these, then a calculator is applied to
compute the difference.

paraview complains that I have not the right data.
Is this problem known? I think the problem is that I have a set of data and
building the difference with a single record seems to be not appropriate.