Measurement factors with underscores result in key error

[JackAtOmenApps]

Because we replace underscores with spaces in _attr_to_unit() in base.py to account for cubic and square values, factor names must not contain underscores or they get replaced and cause problems.

The VolumetricFlowRate below need to be corrected to use dashes vice underscores to resolve this:

miners_inch_50 = Unit("566.33693184e-6", ["mi_50"])
miners_inch_40 = Unit("707.9211648e-6", ["mi_40"])
miners_inch_38_4 = Unit("737.41788e-6", ["mi_38_4"])

[JackAtOmenApps]

Fixed with #66