diff --git a/README.md b/README.md
index 43b00b2..b9d4d44 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,8 @@ So unless you're a retrocomputing enthusiast with such a machine, this is useles
 
 I'm a software guy and know next to nothing about hardware design, so this is very much a work-in-progress and is likely full of rookie mistakes.
 
+To save on PCB cost, the board is smaller than a 'true' SBus board; the directory includes an OpenSCAD 3D-printable extension to make the board compliant to the form factor (visible in the pictures in 'Pictures').
+
 ## The hardware
 
 Directory 'sbus-to-ztex'
@@ -24,4 +26,4 @@ The function embedded in the FPGA currently includes the PROM, lighting Led to d
 
 Directory 'NetBSD'
 
-A basic driver for NetBSD 9.0/sparc, with ioctl to access the LED and GHASH registers, along with a small test code.
\ No newline at end of file
+A basic driver for NetBSD 9.0/sparc, with ioctl to access the LED and GHASH registers, along with a small test code.