What is the meaning of "pr favr" as used in the following examples:

To Cap, Jonathan Clark Woodstock pr favr of Majr Helvinstone ...

To Colo. William Preston Pr Favr. of Mr. Ramsey

To Col° William Fleming Botetourt Pr Favr of Col° Robertson. 

The letter is directed "pr favr Mr Davd Kerr." 

ADDRESSED: To The Honourable Sir William Johnson Bart. pr favr. of the Johnson 
Hall Revd.

I have written you a pacquet of Letters pr Favr of Danl Beale Esq. ...

James Warren Esq Paymaster of the American Army Watertown pr Favr of Messrs Folwell and ...

addressed: "Mrs: A. Adams Grosvenor-Square. London. Pr. favr: of Thos: Martin Esqr."; 

Pr favr of Mr. Basley

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