You can download the PDF to print out your ruler here:
• http://cotswoldjam.org/downloads/paper-gpio-ruler.pdf
In anticipation of our GPIO Zero reaction timer tutorial at our January event (fully booked, sorry), we’ve created some paper GPIO rulers which are very helpful for telling which GPIO pin is which. Identifying exact GPIO pins is a common source of problems in our Raspberry Pi electronics tutorials.
Please make sure you set your PDF reader to print out “Actual Size” – especially if you use US Letter paper, as this document is set for UK/European A4 paper.