Exchange rate query

Hi SAP Gurus,

In OB08 i created 2 exchange rate

Exchange Rate-- -Valid From -- -Indirect quotat Ratio from -direct quo-- ratio --to

1. M--

2.M--

Here the co code currency is USD, now when in try to do F-02 using GBP as the curr then the system is auto picking the exchange rate of direct quo that is 1.50000.

I just want to know how can system auto pick the indirect quo entered

Regards.