potential

likelihood

level

ease

ARO

XL
extra large

AC
almost certain

VH
very high

E
easy

100

L
large

VH

very high

H
high

M
medium

10

M
medium

P

possible

M
medium

D
difficult

1

S
small

U

unlikely

L
low

VD
very difficult

0.1

XS

extra small

VR

very rare

VL

very low

ED

extremely difficult

0.01