diff --git a/README.md b/README.md
index 1b6162a2e42a0055f2b8531314d2e3f4d6b5a125..d0c92f1fa88f018099989f911b93949c67891f4d 100644
--- a/README.md
+++ b/README.md
@@ -57,6 +57,8 @@ measure filtration efficiency and pressure difference with non-biological colloi
 
 could also get away with only one OPC by adding a bypass around the test filter and a switch
 
+Ah - and add in a flowmeter after the second OPC sampler!
+
 
 ## equipment needed
 - nebulizer for aerosolization [^nebulizer]