The domes we build at Cal-Earth primarily use the lancet shape for a variety of reasons, and you need two compasses to achieve this shape.

The height -

Compass determines the placement of bag (its radius) at any given elevation and is a fixed measurement tool which never changes.

The center -

Compass defines the placement of the bag (its radius) along the entire course of a bag. The center compass’s measurement always changes at each new elevation.

Analysis

• Cheap
• Requires a fair bit of skill to operate
• Build crew may waste time waiting for compass operator.
• Prone to integrated errors (a small mistake may invalidate an entire layer or more).

Low cost, low tech solution ideation 

Prototyping the first pipe sail idea. Currently made of bamboo to use less plastic in the prototyping phase.