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Landmarks and Brain Anatomy
Move over a colored region or landmark to see what it means for EEG and sleep staging.
Simulation for sleep tech mastery
International 10/20 System
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Foundation
Why is it called the International 10/20 System?
The name comes from the way electrode locations are measured across the head. Instead of guessing where electrodes should go, the 10/20 system uses anatomical landmarks - like the nasion, inion, and preauricular points - and places electrode sites at specific percentage intervals.
The first and last marks are typically 10% from the landmark endpoints, and the main interior spaces are usually 20% apart. That makes the system reproducible, meaning a technologist in Nevada and a technologist in New York can place electrodes in the same standardized locations.
Sleep tech translation
It is called "10/20" because the map is built from 10% and 20% measurements - not eyeballing, vibes, or "that looks about right."
Move the measurement to see how 10%, 20%, 25%, and 50% distances change from patient to patient.
10%3.6 cm
20%7.2 cm
There are some exceptions to the 10/20 measurement rule. Some measurements require 25% and 50% increments for a full EEG setup.
25%9.0 cm
50%18.0 cm
Electrode numbers tell you the side of the head.
In the 10/20 system, the numbers help identify whether an electrode is on the patient's left or right side.
Odd numbers are on the patient's left.
Examples: F3, C3, O1
Even numbers are on the patient's right.
Examples: F4, C4, O2
Sites ending in z sit on the centerline, also called the midline or zero line.
Examples: Fz, Cz, Pz, Oz
Sleep tech translation
Odd = left. Even = right. Z = center. That rule saves your brain from doing gymnastics at 2:17 a.m. when you are staring at a montage screen.
Centimeters make the math easier and more precise.
The 10/20 system is based on percentages, so measurements need to be easy to divide into 10%, 20%, 25%, or other intervals. Centimeters are used because they work cleanly with decimal math.
For example, if the nasion-to-inion distance is 36 cm:
- 10% = 3.6 cm
- 20% = 7.2 cm
That is much easier than converting inches into fractions or decimals. In clinical work, centimeters also provide a consistent standard across technologists, facilities, and training programs.
Sleep tech translation
Centimeters keep the math clean. Inches turn the lab into a fractions worksheet with electrode paste on it.
See why we use cm? Cleaner numbers, fewer conversion errors.
Game 1
Placement Lab
Place each chip on the correct brain region or electrode site.
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Drag a chip to a target, or select a chip and then select its target.
Game 2
Measurement Math
Practice converting 10/20 placement rules into centimeters.
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