If you have this relationship:
Where the individual readings are in records in PortalTable
Set Variable [ $$MaxAlcohol ; value: Max ( PortalTable::AlcoholSG ) ]
should put the value in a global variable, provided that your portal is not a filtered portal.
My one line portals are filtered. I have a test type field (SG, TTA, ph, and SO2) and I filter portal to show only SG test type. The test result field is a number field. Do you have any suggestions?
a) add a relationship that uses an additional pair of match fields to match to only SG type records.
b) use Max within an ExecuteSQL query with the SG filter criteria replicated as a WHERE clause.