Pivot for Count and count result as percentage of another cell

Hello,

Sorry, struggling to get my head around pivot tables. I'm not sure how to lay out my source data and set up the table I want.

I'm starting off with a one column list of values, 38 rows at the moment, but dynamic. The value can be one of 17 different options.
I can create a Pivot Table that displays a count of each value.

But what I also want is the count as a percentage of another value.

For example my data source (There is no relation between A and B, A is just a list of times the value occours in a database where the records meet certain criteria. There is a relationship between B and C. B is a list of all possible values, C is how many of each value could have appeared in the database.):

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What I'd like from the Pivot Table:

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Can anybody help?

Think I've made some headway. I've now used a CountIf formula in column D to get my data source looking like this:

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With C,D and E set as a list.

I go through the Pivot Table Wizard, and put "Category" in the rows, "Count" in data ---- all works fine.

How do I sort out the percentage? I've tried putting "Count" in the data field again, selecting a "Count2" field and opening Field Settings. If I then click "Options" I can choose show data as: % OF.
But every option I choose in "Base Field" and "Base Item" gives me "# N/A"

Any ideas on what setting I should be using? Am I going the right way by arranging my source data this way?

What's the point of the pivot in this situation? Your table in C:E is already a summary.