# Tip calculator faq

If you own the Tip Calculator I built, this page has info that may be helpful to you. If you have other questions or feedback, email me.
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Here’s the full FAQ…

### What is the Mirror mode?

This setting helps catch if someone’s tampering with your receipt. Let’s say you filled out your receipt like this:

```SUBTOTAL: \$18.50
TIP:       \$3.00
TOTAL:    \$21.50```

Now imagine that evil waiter Joe changes it:

```SUBTOTAL: \$18.50
TIP:       \$8.00
TOTAL:    \$2b.50```

You may think that the letter “b” looks nothing like a 6, but Joe won’t have to write using the Courier font and his forgery will be a tad more realistic.

The `Mirror` mode will adjust the tip amount so that the digits that make up the total are in the same sequence whether they’re read forwards or backwards. check out the receipt shown above, mirrored:

```SUBTOTAL: \$18.50
TIP:       \$2.62
TOTAL:    \$21.12```

By turning the number into a palindrome, you can scan all food charges in your credit card bill and determine if anyone scammed you without doing any math.

Behind the scenes, the App is adjusting the calculated tip either up or down to reach a palindrome, choosing whichever of the two results will change your total by the smallest amount. if you’re concerned about under- or over-tipping while using the Mirror mode, you can tweak the `Tip %` slider appropriately.

### Can you add Tax calculations?

I’ve tried some sample calculations and discovered that typical tax rates have a negligible effect on the total. For example, a meal of \$50 dollars, tipping 18% and with a tax rate of 6.25% would cause a difference of less than 67 cents.

The best feature of this App is this simplicity and the benefit doesn’t seem to be worth jeopardizing it. Obsessive penny-counters don’t despair — I’m exploring a couple of ways of adding tax-awareness to the tip calculator in a way that doesn’t mess with the inferface.

### What’s with the ‘∞’ in the name? Bowtie Infinity?

Pretend it’s a bow tie. I did.

### How can I use the Tip App when everyone in my party wants to tip different percentages?

The best way to do that is to use the `Exact` method, set the tip to 0% and split based on the number of people in your party. The total shown below will be the even split for each person, then, each one in your party can tip as they wish.

### Can you add an option to round up or down?

The app is smart enough to choose rounding up or down — whatever it takes to tip as close as possible to the exact percentage you desire. My rationale is to make the app smart and uncluttered so you don’t have to think about the details of these decisions. Note that if the rounded tip is too different from the tip you desired, you’ll see the `Effective Tip` percentage displayed at the top of the screen.

That’s all for the FAQs for now. If you have any other questions, don’t hesitate to email me. Finally, O’ s/he who loveth the app, I grovel for your reviews.