This is my first instructable so I hope you guys like it!

As a Mechanical Engineer and Product Designer, I always get the best ideas when I am out and about; with none of my tools or gadgets near me. As such, the idea for this instructable comes from being able to have a series of useful tools for creating engineering solutions in your pocket and at your disposal at all times.

The inspiration for this came with the challenge of a contest held on this very site wherein the only requirement was for whatever you were creating to be pocket-sized. Something that I always have in pocket is a pen, and most of the time it is a BIC brand pen. Therefore, I decided to adapt 3 tools that I always use when I am creating to a pen:

Caliper (a device used to measure the distance between two opposite sides of an object)
A center finder (used to find the center point of an object)
A Stylus (to draw on a phone with more precision)

The first two tools require a 3D printer, however once you understand how these are designed, they are relatively simple to make at home with things like scrap wood, plastic, or even cardboard.

Supplies

General:

BIC Brand Pen
Scissors
Superglue
X-Acto Blade

Caliper/Center Finder:

Any color filament (I use PLA)
3D Printer

Stylus:

Copper wire (Aluminum foil can be used an alternative)
Cotton swabs
Water

Step 1: Caliper

A Caliper is normally a large tool which can be used for two purposes:

To measure a distance (as if it were a ruler, but with higher precision)
To lock a distance to use later (without knowing its actual numerical value)

In this case, this hack focuses on the second purpose.

First, 3D print the two pieces that have been included in this step (print one of each).

Once printed, assemble as shown in the images.

Step 2: Use the Caliper

To use the BIC Caliper, hold whatever you are measuring between the two 'beaks'.

This distance will hold and you can transfer it by pressing the tip of the 'beaks' into whatever material you are using.

Step 3: Center Finder

First, 3D print the two pieces that have been included in this step (print one of CenterFinder_P1 and two of CenterFinder_P2).

Once printed, assemble as shown in the images. You will have to superglue the two P2 to P1.

Step 4: Use the Center Finder

To use it, first adapt it to the BIC pen.
Then, place it above the surface you want to find the center of and twist the pen until both long pieces touch either side of the surface.
Move the pen up and down whilst applying pressure to one side to ensure you both long pieces are always touching.
You have now found the center of your surface!

Step 5: Stylus

1- Cut the cotton swab flush on the cotton part

2- Place the copper wire parallel to the stick and secure the connection with adhesive tape. Make sure one end of the wire is in contact with the cotton part.

3- In this step we will check that the connection has been made correctly and we will moisten the cotton. To do this, wet the stick with a little water

4- Next, we will introduce the device that we have created through the small hole of the cap.

5- Now we need to bend the electrical wire in such a way that on the outside of the cap protrudes a little from the wire, so with this last step our Stylus would be finished and fully functional.

Step 6: Use the Stylus

To use our device, we must keep a finger always in contact with the copper cable. In this way our body will generate a load that will travel from the electric cable to the end of the cotton. With this principle the touch screen device will be able to read the pointer.

Tips and reminders

You can use this instrument in several ways. You can use the cap, or the cap set plus the pen for greater comfort and accuracy.

Make sure there is contact between the power cord and the damp cotton!

For it to work properly, the electrical cable must be lightly pressed!