Obtaining Order Currency

How can I find for sure the currency of an order? Because it is not stored directly with orders, and in order data it is stored only the secondary currency (by the way, using a rather criptic letter code, 'R' for currency information). But how can I know the currency the order was created with at the time of its creation? Maybe using the main currency from settings is not a good idea because it can change over time.

Thank you!

At the time of order creation, you can use the CART_SECONDARY_CURRENCY constant in php or $smarty.const.CART_SECONDARY_CURRENCY variable in templates

Thank you eComLabs, but I was refering to obtaining the currency of an order _after_ it was created. In other words, I want to know right now the currency of order x that was created yesterday.

Also, why is that name of "secondary currency"?

Thanks for your time!

Primary currency means base store currency, secondary - used one

You can use

$order_id = 123;
$order_info = fn_get_order_info($order_id);

Thank you eComLabs for your time and help for clearing my mind.

PS: Still thinking those are funny and tricky names.