Why does my formula work in a Chart Object but not in the Script

[#1]

I have a field named Reporting Level that contains the following record categories:

SPA

Parts

Accessories

Demo SPA

Other

Freight

I am only concerned with records that are not SPA, Demo SPA or Freight, as a result, i created the below formula as a calculated Dimension called [Non Spa], and in my pivot table chart , i can select suppress Null Values and then my chart displays exactly what i want.

=IF([Reporting Level]='Spa',isnull,IF([Reporting Level]='Demo Spa',isnull,IF([Reporting Level]='Freight',isnull,[Reporting Level])))

However, i dont want to have to add the above calculated dimension into every chart that i create, so i decided to build this into the script to make this calculated dimension a NEW dimension

but, this formula doesnt work. Why not and is there another solution. I have just started to learn set analysis so i have not been able to put the above into set analysis.

any help is greatly appreciated.

[#2]

Here is your NoSpa

[#3]

Nick,

Thank you for your help, I just added your attached to my script and now the lables are correct in the New field titled 'Non Spa' however the Sales amounts are now all the same which shouldn't be the case. .