An API unit is the usage quota we charge for.
We charge different number of units for different requests. For example, raw data
methods use 1 unit per URL. Thus, when requesting backlinks to a domain, 1
downloaded backlink costs 1 unit. Thus checking 1,000 backlinks for 1,000 domains
equals 1,000,000 units.
Methods providing calculated metrics require 30 units per URL, and the
get-summary
method requires 60 units per URL (get-inlink-rank + get-metrics).