diff --git a/electronics/bom.md b/electronics/bom.md
index 1d5f652..66f486e 100644
--- a/electronics/bom.md
+++ b/electronics/bom.md
@@ -22,9 +22,9 @@ Use transparencies designed for your printer type. The ones I use are Esselte 57
 http://www.123inkt.nl/Esselte-57161-transparanten-voor-inkjet-printers-50-bladen-57161-i22534-t33400.html
 
 ### Circuit board
-I don't use boards with a presensitized photoresist layer, so any plain single or double sided board will do. Don't get the cheap cardboard ones though.
+I don't use boards with a presensitized photoresist layer, so any plain single or double sided board will do. Don't get the cheap cardboard ones though. Be aware that the process is different with the presensitized boards (positive vs negative exposure, different chemicals), so don't follow my guide if you want to etch those.
 
-Adding the film yourself is a bit of extra work, but allows you to retry if the exposure fails. Replacing the film is a lot cheaper than wasting copper.
+Adding the film yourself is a bit of extra work, but allows you to retry if the exposure fails. Replacing the film is a lot cheaper than wasting copper. 
 
 ### Photosensitive film
 Search eBay for "photosensitive dry film PCB". The rolls are blue and typically come in 30cm x 5m.