I like things simple but functional, so I rattled this up for myself. One screen for simplicity, two for when I want bigger buttons and, well, a tip calculator is always handy.
Don't get me wrong it's not something people would pay for (which is why it's not on sale) but it suits me fine.
It works on iPhone as well, not that I use it much, there's nothing wrong with the default iPhone calculator.
Single Screen:
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Split Screen:
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Tip Calculator:
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Name of the app?