Hello @malinthawarnakulasooriya08 ,

It may help you to look at Currency Rate History by Date report. What tables is it using?

Rate Selection screen looks at the document date, then searches the currency tables for the most recent currency exchange rate between 2 currencies -  document currency and base currency -  with a date prior to the document date.

Examples:

For a document in EUR in a USD Base Currency company, dated 3/3/2020, the rate used is dated 3/1/2020, first line highlighted above.

For a document in EUR in a USD Base Currency company, dated 3/6/2020, the rate used is dated 3/5/2020, second line highlighted above.

I think the table you need is CurrencyRate.

Laura

Thank you @Laura02 for the valuable reply.  

According to my requirement after inspecting the screen ASPX I was able to a clue about CurrencyInfo DAC. Then after inspecting the ARInvoice DAC, it was able to find a link between the ARInvoice DAC and the CurrencyInfo DAC through curyInfoID. So by this CurrencyInfo DAC, I was able to get the Rate Selection Effective Date corresponding to the relevant invoice.