Echo of Hero formula?

I think it is just that you add up all your weapon attack and take 4% of that and add it on.

Simply put, if you had 100 total weapon attack, then with Echo you'd have 104 attack.

That would be ((str*4.6+dex)*Watk/100*1.04) or ((str*4.6+dex)*Watk/100*1.02) but neither of those work.