Microscope Use - Coloured Threads
The typical coloured threads (red, green, yellow) microscopy slide demonstrating depth of focus.
Use the fine focus knob on highest power to determine which thread is on top, which is in the middle, and which is on the bottom.
Triarch slide GZ1-2 Version A: (https://www.triarchincorporated.com/)
Video via Leica DM750.