diff --git a/README.md b/README.md
index c8cffad..f494d38 100644
--- a/README.md
+++ b/README.md
@@ -19,3 +19,8 @@ See [FINDINGS.md](FINDINGS.md) for the protocol and calibration notes, and [EEPR
 calibration blob.
 
 Setup: `python -m venv .venv && .venv/bin/pip install -r requirements.txt`
+
+**Calibration cache:** `calib/eeprom_3000.bin` in this repo is the EEPROM dump of one specific mouse.
+`myscan/calib.py` uses that file whenever it exists and only reads the mouse when it is missing. With a
+different mouse, delete it first (`rm calib/eeprom_3000.bin`), so the next scan reads and caches your own
+unit's calibration (about 15 s).