diff --git a/meta-arch/backoffice.png b/meta-arch/backoffice.png
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Binary files a/meta-arch/backoffice.png and b/meta-arch/backoffice.png differ
diff --git a/meta-arch/meta-arch.md b/meta-arch/meta-arch.md
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--- a/meta-arch/meta-arch.md
+++ b/meta-arch/meta-arch.md
@@ -6,10 +6,11 @@ Logical/abstract architecture - to help discuss the non-functional, information
 
 ![Overview](overview.png)
 
-A Mobile app(a) installed on million of devices does regular (e.g. 1-4 times per day) fetches through a common Content Delivery Network (CDN), with no particular integrity or reliability guarantees (best effort).
+A Mobile app(a) installed on million of devices does regular (e.g. 1-4 times per day) fetches through a common Content Delivery Network (CDN), with no particular integrity or reliability guarantees (best effort)[^1].
 
 Fetched is a digitally signed file (c) with the contamination details of the day. This file is generated by a very reliable central backend (d) and contains just the relevant information.
 
+
 At some point (e.g. on a national scale, several 10's to 100's of time an hour) a medical professional will ask if his patient is willing to divulge his contact.
 
 If so - some process is initiated in the backoffce (g) by a medical professional (h). 
@@ -44,3 +45,5 @@ At regular interval (n) aggregators prepare a list for distribution and get this
 
 
 
+[^1]: It will likely be a requirement that the CDN webservers have the Date: header set (RFC 2616, section 14.18) correctly -- as this stabilises the calcuation of 't'.
+