Cannot edit "Expected Revenue" in a potential?

Cannot edit "Expected Revenue" in a potential?

After converting a lead, I checked the option to create a potential and, in potential details, I see a field called "Expected Revenue" which I can't edit. What is its purpose and why can't edit? On "Standard Fields in Opportunities" page from Zoho website, we can see the following description about that field:

"Calculated based on the Amount and potential Stage that you specify". So, how is it calculated? What is the logic for that?