Jeweler's Unit Converter Pro

Jewelers often need to convert between units for price calculations and appraisals, but some of the weight/mass units are esoteric to the industry and are not present in many calculation tools.
Jeweler's Unit Converter Pro meets that need by allowing quick conversions between the following units on the iPad, the iPhone, and the Apple Watch:
AVOIRDUPOIS (Imperial weight):
grain, dram, ounce, pound
METRIC:
microgram, milligram, gram, kilogram
TROY:
carat, pennyweight, ounce, pound
ANCIENT:
Roman drachma, Greek drachma, Israeli sheqel, Chinese tael
You can enter the calculations on an Apple Watch and display the results on a paired iPhone, using the iPhone as a second screen when working with sellers/buyers.