Press on what you want to calculate - with VAT, without VAT or VAT-amount. You will then immediately get the results when you start pressing the numbers or choosing percentage, very quickly and smoothly.
You can then copy each amount by pressing and holding the amount, or export / share all amounts using the share button at the bottom.
Step back with the deletion button or hold it to reset.
Now you can also set your custom percentages by pressing and holding a percent button. The values will be saved when app closes, but there is an option to easy restore the default vat percentages.