How long is a piece of string?

Actually, if you are talking about the quantum physics theory of "superstrings," there is no measure small enough to describe it.  It would be smaller than a muon, even smaller than a neutrino.  (That is, a tad smaller than VC's brain...)

Peace.

Double the length of one end to the middle.

Twice as long as half the length.

Half as long as twice the length.

Monty Python sketch for you:

The scene is an advertising agency office ... the characters are the ad man, Adrian Wapcaplet and the would-be client, Mr Simpson:

W: Aah. Now, I understand you want us to advertise your washing powder. 

S: String. 

W: String, washing powder, what's the difference. We can sell *anything*. 

S: Good. Well I have this large quantity of string, a hundred and twenty-two thousand *miles* of it to be exact, which I inherited, and I thought if I advertised it-- 

W: Of course! A national campaign. Useful stuff, string, no trouble there. 

S: Ah, but there's a snag, you see. Due to bad planning, the hundred and twenty-two thousand miles is in three inch lengths. So it's not very useful. 

W: Well, that's our selling point! "SIMPSON'S INDIVIDUAL STRINGETTES!" 

S: What? 

W: "THE NOW STRING! READY CUT, EASY TO HANDLE, SIMPSON'S INDIVIDUAL EMPEROR STRINGETTES - JUST THE RIGHT LENGTH!" 

S: For what? 

W: "A MILLION HOUSEHOLD USES!" 

S: Such as? 

W: Uhmm...Tying up very small parcels, attaching notes to pigeons' legs, uh, destroying household pests... 

S: Destroying household pests?! How? 

W: Well, if they're bigger than a mouse, you can strangle them with it, and if they're smaller, you flog them to death with it! 

S: Well *surely*! ... 

W: "DESTROY NINETY-NINE PERCENT OF KNOWN HOUSEHOLD PESTS WITH PRE-SLICED, RUSTPROOF, EASY-TO-HANDLE, LOW CALORIE SIMPSON'S INDIVIDUAL EMPEROR STRINGETTES, FREE FROM ARTIFICIAL COLORING, AS USED IN HOSPITALS!" 

S: 'Ospitals!?!?!?!!? 

W: Have you ever been in a Hospital where they didn't have string? 

S: No, but it's only *string*! 

W: ONLY STRING?! It's everything! It's...it's waterproof! 

S: No it isn't! 

W: All right, it's water resistant then! 

S: It isn't! 

W: All right, it's water absorbent! It's...Super Absorbent String! "ABSORB WATER TODAY WITH SIMPSON'S INDIVIDUAL WATER ABSORB-A-TEX STRINGETTES! AWAY WITH FLOODS!" 

S: You just said it was waterproof! 

W: "AWAY WITH THE DULL DRUDGERY OF WORKADAY TIDAL WAVES! USE SIMPSON'S INDIVIDUAL FLOOD PREVENTERS!" 

S: You're mad! 

W: Shut up, shut up, shut up! Sex, sex sex, must get sex into it. Wait, I see a television commercial - There's this nude woman in a bath holding a bit of your string. That's great, great, but we need a doctor, got to have a medical opinion. There's a nude woman in a bath with a doctor--that's too sexy. Put an archbishop there watching them, that'll take the curse off it. Now, we need children and animals. There's two kids admiring the string, and a dog admiring the archbishop who's blessing the string. Uhh...international flavor's missing...make the archbishop Greek Orthodox. Why not Archbishop Macarios? No, no, he's dead... never mind, we'll get his brother, it'll be cheaper... So, there's this nude woman...