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README.md

@@ -16,13 +16,13 @@ configs:
 # QR Scan Difficulty: synthetic codes
 
 The QR codes made for the QR Scan Difficulty page, which measures how many QR codes the scanners in phones can read,
-from clean prints to hard real-world codes. Every image is a synthetic camera picture of a printed code, so its
-content and every condition that shaped it are known exactly.
+on these simulated prints and on codes from four research datasets. Every image is a synthetic camera picture of a
+printed code, so its content and every condition that shaped it are known exactly.
 
 - **tiers**: 1,400 codes in three sets, clean (200), everyday (600) and tough (600), each with its difficulty on
   the page's scale and which of eight scanners read it at seven image sizes.
-- **ladders**: 12,560 codes for the page's "What makes a code hard to read": one code changed one step at a
-  time, 16 factors, 80 codes per step, each with which scanners read it at 1280 px.
+- **ladders**: 13,520 codes for the page's "What makes a code hard to read": one code changed one step at a
+  time, 17 factors, 80 codes per step, each with which scanners read it at 1280 px.
 
 ## How the images were made
 
@@ -33,7 +33,9 @@ digits, filling about 90% of the code's capacity.
 
 Ladders start from one easy code that every scanner reads (version 3, 8 camera pixels per square, sharp, nearly
 head-on) and change a single factor. A seed is the same code in the same scene at every step, so a step changes only
-its factor.
+its factor. `version` keeps the printed size, so its squares shrink as the data grows; `version_big` takes the very
+same codes and scenes and prints them bigger, so every square keeps 6 camera pixels (up to version 21, the largest
+that fits a 1280 × 960 picture at every angle).
 
 ## Fields