You're reading it like this: > GW is [...] a [..] measurement as the amount of energy it stores. Which doesn't parse. If the text read "of" instead of "as", I

You're reading it like this: > GW is [...] a [..] measurement as the amount of energy it stores. Which doesn't parse. If the text read "of" instead of "as", I might agree with you. As it stands, it doesn't correctly parse either way. Given the full context of the statement, the more likely original intention was that: > GW is [...] just a[s] valid and important [a] measurement as the amount of energy it stores.