When you compare the prices of two assets
in a graph
using the US dollar for comparison
(because thats what prices are)
you are using the USD as "a unit of account"
because it is the common unit of valuation.

another example,
people offering to accept payment in BTC
measure the amount of BTC they'll accept in USD
(because thats what prices are)

in these situations,
USD is called the "unit of account"
(because thats what prices are measured on)

and it doesn't change because you do some division in your head.

it isn't anybody elses fault you don't know what words mean. 

 My only point is that this common unit is only so because of the State