diff --git a/keyboards/tutte_coxeter_36k/readme.md b/keyboards/tutte_coxeter_36k/readme.md
index b8b1785d..fc05d105 100644
--- a/keyboards/tutte_coxeter_36k/readme.md
+++ b/keyboards/tutte_coxeter_36k/readme.md
@@ -8,23 +8,31 @@ This is firmware for a Raspberry Pi Pico PR2040 controller monoblock 36 key desi
 [Tutte-Coxeter](https://en.wikipedia.org/wiki/Tutte%E2%80%93Coxeter_graph) graph
 (using only 26 vertices or GPIO pins, with 36 edges or keys - see this
 [blog post](https://astrobeano.blogspot.com/2025/05/ergo-mech-keyboard-wiring-using-tutte-coxeter-graph.html)
-for background, although the final pin selection and trace routing changed):
+for background, although the final pin selection and trace routing changed).
 
-| GP   | 11 | 10 | 3 | 4 | 7 | 26 | 27 | 28 | 15 | 21 | 19 | 20 | 16 |
-|------|----|----|---|---|---|----|----|----|----|----|----|----|----|
-| GP12 |  / |    |   |   |   |    |  F |    |    |    |    |    |    |
-| GP8  |  P |  L |   |   |   |    |    |    |    |    |    |  A |    |
-| GP9  |    |  . | , |   |   |    |    |    |    |    |    |    |    |
-| GP1  |    |    | K | I |   |    |    |    |    |  E |    |    |    |
-| GP6  |    |    |   | M | H |    |    |    |    |    |    |    |    |
-| GP2  |    |  U |   |   | Y |  T |    |    |    |    |    |    |    |
-| GP22 |    |    |   |   |   |  G |  B |    |    |    |    |    | L3 |
-| GP0  |    |    | O |   |   |    |  W |  R |    |    |    |    |    |
-| GP13 |    |    |   |   | N |    |    |  D | R2 |    |    |    |    |
-| GP14 |  ; |    |   |   |   |    |    |    | R1 |  S |    |    |    |
-| GP18 |    |    |   |   |   |  B |    |    |    |  X | L2 |    |    |
-| GP17 |    |    |   |   |   |    |    |  C |    |    | L1 |  Z |    |
-| GP5  |    |    |   | J |   |    |    |    |    |    |    |  Q | R3 |
+This matrix shows the full 15×15 Tutte-Coxeter bipartite scanning matrix with the
+two unused rows and columns last (❌), and the further 9 keys this would allow (⭕) 
+if using 30 GPIOs rather than just 26 for a 13×13 scanning matrix. The allocation
+of keys to matrix elements and scanning matrix rows and columns to GPIO pins was
+arbitrary and down to how best to layout the PCB traces:
+
+| GP | 11 | 10 | 3 | 4 | 7 | 26 | 27 | 28 | 15 | 21 | 19 | 20 | 16 | ❌ | ❌ |
+|---:|:--:|:--:|:-:|:-:|:-:|:--:|:--:|:--:|:--:|:--:|:--:|:--:|:--:|:--:|:--:|
+| 12 |  / |    |   |   |   |    |  F |    |    |    |    |    |    |    | ⭕ |
+| 8  |  P |  L |   |   |   |    |    |    |    |    |    |  A |    |    |    |
+| 9  |    |  . | , |   |   |    |    |    |    |    |    |    |    | ⭕ |    |
+| 1  |    |    | K | I |   |    |    |    |    |  E |    |    |    |    |    |
+| 6  |    |    |   | M | H |    |    |    |    |    |    |    |    |    | ⭕ |
+| 2  |    |  U |   |   | Y |  T |    |    |    |    |    |    |    |    |    |
+| 22 |    |    |   |   |   |  G |  B |    |    |    |    |    | L3 |    |    |
+| 0  |    |    | O |   |   |    |  W |  R |    |    |    |    |    |    |    |
+| 13 |    |    |   |   | N |    |    |  D | R2 |    |    |    |    |    |    |
+| 14 |  ; |    |   |   |   |    |    |    | R1 |  S |    |    |    |    |    |
+| 18 |    |    |   |   |   |  B |    |    |    |  X | L2 |    |    |    |    |
+| 17 |    |    |   |   |   |    |    |  C |    |    | L1 |  Z |    |    |    |
+| 5  |    |    |   | J |   |    |    |    |    |    |    |  Q | R3 |    |    |
+| ❌   |    |    |   |   |   |    |    |    | ⭕ |    |    |    | ⭕  | ⭕ |    |
+| ❌   |    |    |   |   |   |    |    |    |    |    | ⭕ |    |    | ⭕  | ⭕ |
 
 The keys here are labeled as per Qwerty, with L1, L2, L3, R3, R2, and R1 for the thumbs: