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# A 10-key is an adding machine (many of which print this nice little tape for you as proof that you add  staggering columns of numbers correctly).

Its sole function is to add numbers. Positive numbers, negative numbers, all kinds of numbers. If it's of decent quality, it will even tell you how many numbers!

The item count is a neat feature that can also stupify if you haven't had much experience with a ten-key--or if you just didn't bother to read the instructions that came with your calculator. However, I'll explain all that in a few moments.

# Adding numbers on a 10 key

10 keys are not as intuitive as you might think. For those just learning how to use a 10 key, here is a simple addition problem step by step.

6+5+9+8

First, open up your PentaCalc 10 key software:

1. Press: [ 6 ] [ + ] [ 5 ] [ + ] [ 9 ] [ + ] [ 8 ] [ + ]
2. See your total in the live tape reel? It should show 28. If it doesn't, clear things and start over at #1 above.

# Adding and subtracting numbers on a 10 key

If you think adding was easy let's mix things up a bit. Let's try add and subtract some numbers.

6+5-9-8

1. Press: [ 6 ] [ + ] [ 5 ] [ + ] [ 9 ] [ - ] [ 8 ] [ - ]
2. See your total there on the screen now? I hope it shows —6. If it doesn't, start over.
The thing to remember here is that the calculator is going to ADD everything you input with the keys. So if you want to subtract something, you have to enter it as a negative number or, if it's easier to remember, think of it as telling the machine you want to add into the total the number 6 you just entered, you want to add in the 5, take away or subtract the 9, and take away or subtract the 8. But you can't tell the machine to do these things with a number until you've entered the number itself!

# Another way to think about a ten key

Here's a short bit of further clarification for those who still might be having trouble with this concept. Think of it like this. You've just punched in a [ 6 ], now you have to tell the ten key what to do with it, so you punch in a [ + ], then the [ 5 ], and you have to tell it what to do with that one, which again is to add it, then the [ 9 ], which you must tell it to subtract so you follow with a [ - ]!

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