Today I saw in my English class that the phrase "Bob's your uncle" is used to say when the people reach an objective, for example:
My house is in Mexico City, at Eje Central, you go to the Torre Latinoamericana, turn to the left, straight ahead in that street, pass three streets, turn to the right, straight ahead four streets and Bob's your uncle!
Another example would be:
To make hotcakes, you should shake two eggs with 15 oz of flour, mix it with milk, cook them on the stove and Bob's your uncle
My question here is, Why the translation of these phrase is too different with the usage? Is there a legend or a story about that phrase?