diff --git a/README.md b/README.md
index 9fcde34..98fa4f9 100644
--- a/README.md
+++ b/README.md
@@ -25,3 +25,20 @@ Firmware images can be built via the Makefile in the firmware subdirectory.  The
 * 1:off 2: on - 16-sector firmware (0x0100)
 * 1: on 2:off - 13-sector firmware (0x0200)
 * 1: on 2: on - firmware "put jumpers here" splash screen (0x0300)
+
+## Calibration procedure
+
+* set J4 to off/off ("controller test firmware")
+* connect oscilloscope to TP1
+* start machine
+* execute "call 50688"
+* execute "AAW" (and immediately hit ESC)
+* adjust R1 until waveform period is 5.4 microseconds
+* connect oscilloscope to TP2
+* execute "99W" (and immediately hit ESX)
+* adjust R2 until waveform period is 3.8 microseconds
+* card is now calibrated, power off machine and set J4 to "16-sector firmware"
+
+## Construction notes
+
+* J3 can be omitted if this controller is used with a FloppyEmu