diff --git a/builders/bbh_michigan_monthly.py b/builders/bbh_michigan_monthly.py
index 4203bcc..ace1046 100644
--- a/builders/bbh_michigan_monthly.py
+++ b/builders/bbh_michigan_monthly.py
@@ -31,7 +31,9 @@
 
 Network cost: the deposit is a single 189 MiB zip. This builder HTTP-range-reads
 the zip's central directory and then only the three compressed members it needs
-(~310 KiB), falling back to a full download if the host stops honouring Range.
+(824,944 bytes transferred in total, measured -- each member is read through a
+256 KiB buffer, so reads overshoot the ~310 KiB of compressed member bytes),
+falling back to a full download if the host stops honouring Range.
 
 Stages: fetch -> pre-process -> validate -> write.