Setting Default Currency for Custom App

Hello

How does frappe determine the default currency to use? (I am just using the framework not erpnext)

I created various reports, eg:-

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When I show on a dashboard using a card it will only display in GBP if I disable all the other currencies in the Currency doctype. (This is not ideal as I also want to use EUR)

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As soon as I enable another currency, the dashboard currency is wrong.

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My default language and country is United Kingdom etc…any ideas?