This is my best trick! I invented it in 1984 and has sold many, many hundreds over the years, it is always a hit at magic conventions. I have liking for doing "ungimmicked versions" of tricks, that are normally performed using gimmicks. This one of those.
Two effects:

PROFESSORS NIGHTMARE IN COLOR
You show thre unequal ropes, one is red, one is blue and one is yellow, counting them from hand to hand. With one simple tug, you make the ropes equal!
LINKING ROPES
Two spectators each choose a rope and you take the remaining one and you all tie a knot in the rope making a circle, a ring of rope. You gather the three rope rings in your and try to pull them a part, but they are linked to each other! The ropes are real, the knots are real and everything can be examined.
No magnets, no extra pieces of rope, NO GIMMICKS! Only knowledge is used. You receive three ropes in different colours, an illustrated instruction PLUS a dvd showing the effect and in detail, step by step, teaching you how to setup and perform the effect.

Bonus effect: ORDER OF YOUR THOUGHT
The spectator may tie the ropes in any order he likes, formig a long rope. You have a red handkerchief visible in your breast pocket.You pull out the handkerchief and there are two more handkerchiefs, all three in the same colours as the ropes, and tied to each other in the same order as the ropes. For this bonus effect you can use your own silks (not included).

You can perform on, two or all three effects in a sequence. Easy to learn!