diff --git a/doc/units.txt b/doc/units.txt
index 43d27e70c..b166a9f13 100644
--- a/doc/units.txt
+++ b/doc/units.txt
@@ -16,4 +16,7 @@ conductance       µS
 capacitance       nF
 firing rate       /s
 phase/angle       deg
-================= =====
\ No newline at end of file
+================= =====
+
+Synaptic weights are in microsiemens or nanoamps, depending on whether the post-synaptic mechanism implements a change in conductance or current.
+Distances are typically in microns, but any distance scale can be used, provided it is used consistently.