Typing a % symbol every time to input a number doesn't make a percent either.
I never said that, maybe a misunderstanding.
Here is what I have now:
Just following Appendix C and putting a suffix % in the format.

When you enter the value in the form, you have to specify the '%' as part of the input. The object is saved and field is is displayed '10.00%'.

If you don't specify the '%' symbol at the end only '10.00' you get an error

As you can see, user has to put the % in every attribute that has the '%' symbol in the format.
Using my attribute with the % specified in format (1st pic):
When using this attribute in calculations, the attribute is calculated as a percentage.
Object.Price = $20
Rule (Works):
Object.Price_Total_incGST=Object.Price_Total*SystemSettings.GST+Object.Price_Total
Object.Price_Total_incGST=$22
Is the above rule not supposed to work like that?
Now, If the format in the GST attribute does not contain % suffix.
The calculation would simply be: Price_Total*SystemSettings.GST+Price_Total
Object.Price_Total_incGST=$220
ii) Are you advising to leave all my % based number attributes in the Object like GST, discount, surcharge, TAX etc.. as a number without using the format input & have a rule for each & when using in calculations, just use rule:
Object.Price_Total_incGST=(Object.Total_Amount*(SystemSettings.GST / 100))+Object.Total_Amount
Just to be clear, my observation regarding the $ and % in format are by no means of 'show stopper' proportions, in my opinion, its merely a 'user experience' nuisance from the front-end user point of view, having to manually enter the % symbol for each of those inputs that require it (as shown in the pics).
Would love to see examples of how someone is using the percentage fields in their apps without using the format input in the attribute.
Cheers