1. Using Processing

Give new users an easy interface to work with. One that is not as scary as the serial monitor. 

We have a video that shows the process 

https://youtu.be/jgk8L8_pWiU

Follow this link to the full guide and all details

UI design for the calibration app
UI design for the calibration app
https://youtu.be/ONg3iwaVUks

2. Using desktop App by @Jason Snow  

Try this desktop App it will ask you to install .NET Framework 3.5

It is like the mobile App but on your PC using USB to send all commands

3. Using Otto Blockly with the calibration block

The most simple way so far but annoyingly need to reupload the code until by iteration you achieve the right alignment of the motors

It is a default example in Otto Blockly ready to open

Change the legs and feet values gradually with small values and increments(+5 or - 5 degrees)

Iteratively you have to check/upload the code multiple times, until Otto legs and feet looks completely straight.

Read this article for more details: https://www.ottodiy.com/blog/calibration

4. Using Otto Blockly with serial monitor for assistance and adjustment

I just made this "basic" example of how to quickly calibrate Otto servo motors, we have seen very good methods here with Arduino IDE, but this one aims to make it simple for beginners.

Just open/upload then start serial monitor and follow the instructions.

Calibrate Otto with serial monitor in Otto Blockly
Calibrate Otto with serial monitor in Otto Blockly

It is very handy because is fast and easy to leave your Otto perfectly calibrated in one upload.

But It needs improvement and actually, I found out we are missing blocks for it so we will need to create new blocks just to make this example work, 

missing on variables int8_t  and uint8_t  

need Otto._moveServos(10, array variable); block

5. Using Arduino Serial has been always the way to do it

Upload this sketch OttoDIYLib/examples/calibration  upload the code, then  open serial monitor and follow instructions. But is quite advanced process for many, even do with a proper tutorial is not that hard.

serial monitor does all the work for you
serial monitor does all the work for you