This handy tool is beneficial for fly fisherman. This unit will be your buddy in Icy Fly Fishing waters when you have cold finger tips.

Also, if you do not feel your leader tip between your fingers due to failing nerves in your fingertips (for example when you have diabetics), this tool will help you to tie the knot you need.

For instructions/explanations:

Click on the 2nd picture on your laptop/computor screen to enlarge it. Open your( iPhone/Android) camara to scan the QR-code and it will lead you to serveral knot instructions

Or see Youtube :