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# A 10-key is an adding machine with a tape for proof that you add columns of numbers correctly.

A 10-key calculator's sole function is to add/subtract numbers. Positive numbers, negative numbers, any kind of number.

# Adding numbers on a 10 key

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

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 the tape reel and start over.
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# Adding and subtracting numbers on a 10 key

Think adding was easy? Let's mix things up a bit. Let's try adding and subtracting some numbers.

6+5-9-8

1. Press: [ 6 ] [ + ] [ 5 ] [ + ] [ 9 ] [ - ] [ 8 ] [ - ]

2. See your total there on the screen now? Hopefully, it shows -6. If it doesn't, start over.

The calculator is going to ADD everything you input with the keys. If you want to subtract something, you have to enter it as a negative number. 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.

# Another way to think about a ten key

Still 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 the 6, so you punch in a +. Then you punch in the 5 and you have to tell it what to do with the 5, which again is to add it. Then you punch in the 9, which you must tell it to subtract so you follow with a -.

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