Context
It is the unit contribution: it serves as the basis for any other amount. The one who buys the dollars pays the bid rate; The one who sells them to you charges the one who sells them.
For historical reference: a week ago (06/11) US$ 1 cost $ 1.555,00 (+0,96%); a month ago, $ 1.550,00 (+1,29%); over the last 30 days the range was $ 1.545,00 to $ 1.575,00 (daily selling data from argentinadatos.com).
Keep in mind: It is an illegal, unbacked market: the published price is a reference average and each trade may vary, plus there is a risk of counterfeit bills or scams.
The other way around? Passing pesos to blue dollar.