d18 Tai Xuan Jing die (hollow)

NOTE: This is the hollow version of this die. The solid version can be found here: https://www.shapeways.com/product/ABCXDL6AL/d18-tai-xuan-jing-die-solid
This die can be used to cast to build the 81 ternary tetragrams ofTaixuanjing (太玄經) which translates to "Canon of Supreme Mystery".
Tai Xuan Jing is a method of divination somewhat similar to I CHING. Please see also my I CHING dice and other divination dice here: https://www.shapeways.com/shops/oddball?section=Divination+Dice&s=0
Each line can be solid, broken once, or broken twice.
The odds are assumed to be 4:4:1 for solid:once-broken:twice-broken respectively
These odds could be determined using nine sides, but since odd numbered dice are tricky to design, I've duplicated the odds (8:8:2) and used an 18 sided trapezohedron die with each result listed twice.
Casting this die four times will generate a single tetragram. 
You can read basic info about Tai Xuan Jing here:
https://en.wikipedia.org/wiki/Taixuanjing
You can read about the probabilities of casting here:
https://www.russellcottrell.com/VirtualYarrowStalks/TaiXuanJing.htm