Tax field should be added!!! – Tip Calculator % Pro Review

This is the best I've tried - sliders to enter data vs. "tediously" keying in digits one-by-one in ALL other apps. But other reviewers are right, pre-tax subtotal MUST be an option for proper tipping etiquette and to save time! PLEASE update this app to do so!
Review by DocuGuy on Tip Calculator % Pro.