5

Press these keys on iPhone calculator:

5 + 5 =

Unsurprisingly, the answer is 10. But keep on pressing the = sign and this is the output:

10, 15, 20, 25, 30, 35, 40, 45 … and so on

Why is this useful?

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7

It's an auto-constant
Whether or not you find it useful depends on what you want to do.

Your method of just hitting = over & over just repeats the last calculation, so
2 * 2 = 4 = 8 = 16 = 32 etc

But, say you needed to calculate tax on a set of payments at 15%

If you want just the tax, type
100 * 0.15 =
then your amounts
87.20 = 13.08
43.57 = 6.55
12.50 = 1.88 etc..
If you wanted the amount including tax, you'd start with
100 * 1.15 = & off you go with your amounts, as above...

From comments - this function has been on calculators [in slightly different ways] since at least the mid-70s. It's not a new feature.
On the early ones, 2*=======... would quickly just ERR. Since then they've got somewhat more flexible & move to scientific notation.

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4
  • 5
    I think it's important to note that this has been on calculators pretty much since the time they were digital. I remember it being there in the early '80s.
    – Allan
    Aug 19, 2017 at 15:09
  • 2
    For sure, it's been there a long time, my 70's LED Texas did it - though surprisingly not on all & not all work the same way round. I've known my tax example to need 0.15*100= to kick it off.
    – Tetsujin
    Aug 19, 2017 at 15:10
  • My HP19B needed something to prime the pump as well. Just found a video of a hack to the = button on a cheap calculator turning it into a counter: youtu.be/VLAv7cNCB3U
    – Allan
    Aug 19, 2017 at 15:15
  • 1
    Wow... does that guy need to employ a cameraman ;) but yeah, neat idea.
    – Tetsujin
    Aug 19, 2017 at 15:17

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