What is the exact use of a M button in standard Calculaters? How to keep any digits in memory?

Question

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Answer 1

M button is to put the last number visible in memory. How to retrieve that number after that it's not visible? Press M again or sometimes MR would be it.

Answer 2

Most calculators that feature an M button come with several others. Here's a breakdown:

M+ : Store current entry into memory.
MR - Memory Recall: Retrieve entry stored in memory.
M- : Remove entry from memory.
CE - Clear Entry: Clears the current entry displayed on the calculator
C - Clear: Clears the current entry and zeros out the calculator. Numbers in memory do not get erased.
CA - Clear All: Clears the current entry and all entries in memory, and zeros out the calculator.

When you're using a calculator, you could, for example, perform a bunch of steps to arrive at a number. Once the calculator displays that number, you press M+ to store it into the calculator's memory. After that, you can use C to zero out the calculator and do something else. At any time, you can use MR to put the value you stored in memory onto the display. This way, you don't have to write a number down with a pen and paper in order for you to work with it later. If you no longer need to use the value you've stored in memory, you can press M- to remove it, or press CA to remove the value from the memory and also clear the entry and zero out the calculator.

Play with a calculator a little bit. Once you know what the buttons are for, memory is really easy to use.