diff --git a/lrftubes.lyx b/lrftubes.lyx
index d5d8564..2d9ff05 100644
--- a/lrftubes.lyx
+++ b/lrftubes.lyx
@@ -7918,7 +7918,7 @@ Radiation impedance of a baffled piston
 \begin_inset Formula $\pi a^{2}$
 \end_inset
 
-
+ cross sectional area [m^2]
 \end_layout
 
 \begin_layout Standard
@@ -8274,7 +8274,7 @@ in which
 status open
 
 \begin_layout Plain Layout
-TO DO: redraw image
+TO DO: redraw image and list what approximations are used
 \end_layout
 
 \end_inset