# Where does a calculator get a random seed from?

Most, if not all, scientific and graphing calculators have a #RAND button on them, this generally generates a random number between 0 and 1 (I think).

Now, as we all (might) know, a calculator is a computer, and thus thinks in logic and cannot generate a truly random number, and, as we also (might) know, any pseudo-random number generated has to come from a seed value.

Some things take it from the time and date, others from the time between a user's input, I have even heard stories of a program asking a used to 'bash wildly on the keyboard like a monkey'. So my question is this:
Where does my calculator get its seed value from?

By the way, I cut it into paragraphs to make it more readable

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8 years ago
Each calculator/cpu/software has its own method I'm pretty sure a lot of them seed with # of milliseconds since cpu turned on. # of bytes of ram used, rom used, time since last button press, even random things if they have sensors like temperature of the cpu. The sum of all the variables in the system, etc.
Since your calculator already has the ability to store several numbers in memory, I suspect that it has a special storage location for the last random number generated and that it uses this as the seed.

To test this theory, try this:
• Take the batteries out of your calculator (including any backup battery).
• Replace them and turn it on
• Generate one random number without pressing any other buttons
• Repeat the previous three steps
If the seed is stored as I suggested, you should get the same number both times.

8 years ago
By the way, if you are paranoid about randomness but cannot afford to buy a real random number generator for your computer, you can always borrow a cup of freshly digitized entropy from some friendly particle physicists.
8 years ago
Or Random.org generates them from atmospheric noise (radio static).
munchman (author)  NobodyInParticular8 years ago
Not worried about it, just interested.
NachoMahma8 years ago
. The numbers are not truly random. Your calculator uses a Pseudo-Random Number Generator (PRNG), usually shortened to Random Number Generator (RNG).
8 years ago
Yes, munchman said it was pseudo-random in the question.