Foot (' ') and inch (" ") marks have been commonly confused for single (‘ ’) and double (“ ”) quotes for decades on the Web. Years ago, a student of mine explained the difference.

The Foot Mark vs Single Open and Single Close Quote

The foot—better referred to as prime—mark should not be used to show possession or to contract words. For example, using a foot mark to show possession in Shostakovich's 10^th Symphony or in the title Max's Kansas City is wrong. It's also wrong to use the foot mark in a contraction, as I'm using in this sentence.

The foot mark is only to be used to indicate feet. For example, I stand 5'7".

Modifying my examples above, it’s correct to say that Shostakovich’s 10^th symphony is superb, Max’s Kansas City was a groundbreaking club in NY during the 60s and 70s, and that single close quotes should be used in contractions, as I’m correctly using them now in this sentence.

The foot mark is also incorrectly used as a single open quote: John Lennon once said, “Paul once told me, 'I'm dead'.” Revising the previous quote to use the correct single open and close quotes, Lennon did say, “Paul once told me, ‘I’m dead’.”

See the table below for the keyboard shortcuts associated with foot marks on your keyboard.

The Inch Mark vs Double Open and Double Close Quote

The inch mark should not be used in place of quotes; it should be used to show length in inches. Thus, if I quote Leonardo da Vinci as having said, "The time will come when men such as I will look upon the murder of animals as they now look on the murder of men", with inch marks, then I’ve done a disservice to both the rules of type and the quote.

The correct usage of the inch mark and double open and close quotes follows: the vegan basketball player John Salley, who stands at a towering 6'11", very likely agrees with what Paul McCartney once said: “If slaughterhouses had glass walls, we would all be vegetarian.”

So, as Ellen Lupton once said, “Know thy keystrokes!”^*

Windows Keystroke Instructions

Unlike the Mac keystrokes, where you’ll hold down two or three keys at one time to achieve the proper punctuation mark, in Windows, you’ll need to hold one key down while sequentially typing three number keys. For example, if I need a single open quote (the first entry in the table below), I would hold down the ALT key and then sequentially type the numbers 0, 1, 4, and 5 on the numeric keypad — not the number row along the top of the keyboard.