You can create "Set" from University Filed.
Then create calculated field.
// Float is to make the field type to dicimal number to make the axis synclonized
FLOAT(if [Selected Univ.]then [Overall Score] end)
You can change the University in the list with editing the Set of "Selected Univ.".
ExampleWorkbook_SM_9.3.twbx 37.4 KB
Unfortunately when I try your suggestion, my set of universities display as separate lines on the chart, rather than one line showing the average of the set (I tried changing the Measure from Sum to Avg, but this hasn't worked). I have looked at the example workbook you sent back, but I can't work out out how made the Selected Univ. set show only as one line? Am I missing a step? Many thanks for all your help!
Thanks for all your help, Shin. It was because the University pill was in the Measure Values card. Once I took that out, it was fine.