Counting unique text entries by first 3 letters

See the attachment.

formula
for unique values

Formula:

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number of unique values for

Formula:

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Sorry for off-topic interjection:

@Czeslaw

Although there is no official rule regarding this behaviour, we request that wherever possible both the question AND the answer be provided in substantive detail here within the thread. An attached workbook is an excellent aid for posing a question and offering a solution, but solely doing that with no in thread explanation makes it difficult for researchers to understand or consider the Q & A of this thread without downloading what may be a pointless doc to them, if they can do that at all. Doing that also hides the content from search engines so others may never benefit from this.

I'm sure you understand, and we look forward to seeing you post your formulas/macros in your posts for the searching benefit of all.

Thanks again for all your hard work here!