Picture of Lego Mindstorms Calculator
This calculator uses a modified version of one of the Mindstorms tutorial's code to add how many times you press one touch sensor to how many times you press another touch sensor. To subtract, you have to add negative numbers.

Oh and sorry for the poor picture quality, I took everything on an iPhone camera :P
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Step 1: Parts

Picture of Parts
Two touch sensors
8 black pegs
2 "L" bars
Mindstorms NXT brick
2 connector cords for sensors

Step 2: Add the L bars

Picture of Add the L bars
Attach the L bars to the NXT with the little peg things.

Step 3: Add the sensors

Picture of Add the sensors
Attach the sensors to the L bars with the leftover peg things.

Step 4: Plug the sensors into the NXT

Picture of Plug the sensors into the NXT
Plug the left sensor into port 1 and the right sensor into port 2. I put two longer pegs in the NXT to keep the wires in place, but it won't affect anything if you leave them out.

Step 5: Download code

Download the 2 files on this page and sync "add.rbt" to your NXT brick. 
felinski4 months ago

New download link? Original doesnt work

ALogan97 (author)  felinski4 months ago
I honestly have no clue where the original file went and don't have the NXT software to reconstruct it after going through a couple laptops since using it, sorry. From what I am recall, though, it was a pretty simple thing with one touch sensor incrementing a variable and the other decrementing, but I don't remember how I switched from first to second number or added them afterwards. Might have been something like posting both sensors simultaneously or something? If you feel like getting something working off that and post it, I'll update crediting you.
felinski ALogan973 months ago
I searched a bit on the lego forums and found some other calculator programs. Most of them were built in the way you described them.
I can understand why you don't have the file anymore, this was posted a long time ago, lol. It's a bit weird because googling NXT calculator brings up your instructable as one of the top 5 answers.
For anyone stumbling upon this, here is a link to the lego forums calculators:

Anyways, thanks for helping me out.
AJMansfield3 years ago
Wow that sounds so incredibly useful!
jbarrett93 years ago
Cool I personally don't have nxt but just to see it in action can you put avid up
ALogan97 (author)  jbarrett93 years ago
Yeah, I'll probably have one up in a few weeks after I rebuilt it
khsora4 years ago
=0 cooooollllllllllll!!!!!!!!!!!!!!!! xD
Dude im getting the computer soon probaly gonna make a whole bunch of things