Denim is mostly associated with right hand twill. The most common method of weaving denim. It is easy recognizable when looking at the back side of the fabric. The fabric structure shows a diagonal weave.
However, a very common problem with right hand twill was and still is the twisted leg. Twisted leg occurs especially with non sanforised denim when the denim is worn and washed. The fabric shrinks and turns in the direction of the weave leaving the side seams in the middle of the leg.
By the late 50s and early 60s fabric mills tried to avoid twisted legs on denims by using broken twill denim. Here the direction of the twill is reversed on a regular basis. It is easy recognizable by its zig zag pattern on the back side of the fabric.
Fabric engineers back in the days hoped to solve the twisted leg with this. Not only has the fabric a special look to it but also it feels softer and more comfortable then normal right hand twill denim.