# Calculators and their functions

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May I start by saying this is not a college course. In GB now we are expected to carryout about 3 hrs per year CPD training with regards to our jobs, its a government requirement. I see the benefits of it as our vehicles are all fast becoming high voltage electric vehicles which are or can be very dangerous in the wrong hands.

I am a qualified auto-electrician by trade and been in the job some 30 years, but not as a specialist as I carryout other areas of work routinely.

So I'm doing some research and I have been refreshing my understanding of determining resistances in parallel circuits. I like knowing I can work mathematics out on paper rather than using a calculator, but having half a dozen calculators I can't seem to get the understanding of this calculation where the author is using a calculator but does not tell us what make and model it is!

It is a simple enough calculation but the author shows it like this;

1 divided by 3 M+

1 divided by 4 M+

1 divided by 6 M+

divided M_RC =

I know the answer on paper is 1.33 ohms but using calculators I can't get anywhere near that solution. I have books on the calculators I have but they don't show how that type of sum is work out!

Has the author missed some steps?

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22 minutes ago, Casio said:

1 divided by 3 M+

1 divided by 4 M+

1 divided by 6 M+

If I do that on my calculator (just the app on my laptop) I end up with 13 in the calculator memory (ie. 3+4+6).

If I change it to:

1 divided by 3 = M+

1 divided by 4 = M+

1 divided by 6 = M+

Then I end up with 0.75 in the memory.

I don't know which of those was intended.

22 minutes ago, Casio said:

divided M_RC =

I don't even know what that is supposed to do.

If I literally follow the instructions then, at this point, I am left with 6 displayed on the calculator and so if I do "divide memory-recall =" then I end up with 0.46 (6/13)

I have no idea what the calculation is supposed to be, so I don't know how you end up with 1.33 or what a correct sequence on a calculator would be.

3 minutes ago, Strange said:

I have no idea what the calculation is supposed to be, so I don't know how you end up with 1.33 or what a correct sequence on a calculator would be.

Ah, just spotted the reference to parallel resistors.

So on my calculator, the correct sequence would be:

MC (clear the memory)

1 divide 3 = M+

1 divide 4 = M+

1 divide 6 = M+ (at this point the memory contains 0.75)

C (clear, may not be necessary but just to be sure)

1 divide MR = (1 divided by memory-read)

This results in 1.3333

Does that help?

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Thanks, it's something to do with the instructions when using a calculator that I'm not understanding. I have a Casio fx-85GT plus, and a TI30XA Texas calculator and both books for me don't make it clear how to use the memory function for more than one operation on the same calculation. I had similar results to your previous ones myself but your last result is correct, however, it won't work on these calculators I have for some reason!

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It doesn't look as if the instructions map directly onto those. I can only suggest reading the instructions for those calculators.

I have just looked at a picture of the Casio fx-85gt and have to say it is not immediately obvious how you get values in and out of the memory! I assume you use M+ to store into the memory and maybe Alpha-M+ to read it? I guess it gets cleared when you press AC.

The TI doesn't seem to have a memory function at all. (I'm sure it has, but it is probably not a simple memory.)

Maybe buy a simpler calculator on eBay?

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Posted (edited)

I am not familiar with either of those models.

However I do know that my old Ti-60 works entirely differently from the modern school calculators, and I have an even older National Semiconductor that works in true Reverse Polish.

I can't get on with my daughter's Casio fx-83 (as bought in a supermarket) and she doesn't like my Ti-60.

Edited by studiot

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