99% of the time a parameter is used for user selection, but even in this case I think you would be better off with a calculated field to do the calculation and return the weighting value for that day.
if the Parameter has one value for each day (7 each). would I then need to have seven static calculated fields?
I'm still missing your point - I don't think you need a parameter at all - UNLESS the user is choosing the day for comparison reasons, and then you just reference the parameter in the calculated field.
Can you create a mockup of your situation in the demo database and post it ?
each of day of week has a different value (one time set-up)
one thought is to have the user select the desired day of week (parameter - but the user said they don't want to)
so I suggested that I could grab the day of week (today()) and do a "lookup" on a "setup" table and grab the value associated with this and use in the Calculated Field...
so my thought at the moment is where to look for SetUp table (in Excel i'd make a range, in VBA an array, etc.), but how best to do in Tableau (I know I could make seven calculated fields, but...)?
No, just one calculated field with this code :
CASE datename('weekday', today()) when 'Monday' then 1 when 'Tuesday' then .8 when 'Wednesday' then .6 when 'Thursday' then .4 when 'Friday' then .2 when 'Saturday' then 0 when 'Sunday' then .5 END
then just reference that when you want to include the weighting.