How to Read Base Units and Unit Types
As discussed in the SI discussion, a SI base or derived type is used
for each category. Each unit type within a category is expressed as that base
or derived type. Look at the following screen shot.
We selected the AREA category and wanted to convert from 13.22 "acre (US survey)"
to hectare. You can see the result is 5.34996559.
You can also see the base or derived type for AREA is the "square meter."
One "acre (US survey)" comprises 4046.87260987 square meters.
A hectare comprises 10000 square meters.
Since "acre (US survey)" and "hectare" are expressed as "square meters" it is easy to do the conversion.
In the example below, notice the precision is set to 8.
In other words, 13.22 "acre (US survey)" is approximately equal to 5.34996559 hectares.