How to get the chosen currency rates in admin module

[dolec]

I develop module where i have input value fields in config - those are in one currency. How can i get the chosen currency and rate (php) and or save those input files in given currency so when using it later in other calculation presta knew the currency saved

 

Now i use such method to updtade the float with value

 

Configuration::updateValue($this->name.'_message', Tools::getValue('our_message'), true);