I don't know how to explain the context. Two people are speaking about the Budapest oil deal of 1931.
Kurt to Teck: "You too wish to go back to Europe?"
Kurt: "But they do not much want you. Not since the Budapest oil deal of '31."
Teck: "You seem as well informed about me as I am about you."
Kurt: "That must have been a conference of high comedy, that one. Everybody trying to guess whether Kessler was working for Fritz Thyssen, and what Thyssen really wanted--and whether this 'National Socialism' was a smart blind of Thyssen's, and where was Wolff. I should like to have seen you and your friends. It is too bad: you guessed an inch off, eh?
Teck: "More than an inch."
Kurt: "And Kessler has a memory? I do not think Herr Blecher would pay you money for a description of a man who has a month to travel. But I think he would pay you in a visa.
I think it means "- You began to guessing a little? - Not a little" I couldn't find any dictionary entries about "guess off" or "guess an inch off" though.