I meant just go to your Weight view parameter and type in a number, like 1234.56789 to see if the formatting is working correctly. In a session, that param is probably being supplied into the view so it should work there
Like so:
and finally,
Also, I just found out that you need to select Pattern from the first dropdown to get the Format Pattern text field to be editable - when it's set to Number, it'll be greyed out, regardless if you parameter is a number and if you set it to Pattern, it should be editable, regardless if your parameter is a number.