Hi Amr,
The 1st local currency exchange rate is defaulted by SAP and you cannot change it. SAP has defaulted it to avoid exchange rate difference in the system.
When posting and clearing documents the system uses type M for translation. You can see exchange rates defined at global level in OB08. See the settings in Netweaver>general settings>currencies>enter exchange rates.
" The system uses the type M exchange rates for foreign currency
translation when posting and clearing documents in the activity Enter
Exchange Rate. An entry must exist in the system for this exchange rate
type. The exchange rates apply to all company codes."
However you can maintain different exchange rate type in automatic payment program or revaluation.
Regards,
Unnivel