diff --git a/Performance.md b/Performance.md
index 8ff750c..f8c3485 100644
--- a/Performance.md
+++ b/Performance.md
@@ -61,6 +61,9 @@ The munin
 [/tahoe-figleaf-graph/hanford.allmydata.com-tahoe_speedstats_delay.html delay graph] and
 [/tahoe-figleaf-graph/hanford.allmydata.com-tahoe_speedstats_rate.html rate graph] show these Ax+B numbers for a node in colo and a node behind a DSL line.
 
+The [/tahoe-figleaf/graph/hanford.allmydata.com-tahoe_speedstats_delay_SSK.html mutable-file delay graph] shows the "B" per-file latency number
+for mutable (aka "SSK") files. In the 0.7.0 release, this is dominated by the RSA keypair generation necessary to create each new mutable file.
+
 The 
 [/tahoe-figleaf-graph/hanford.allmydata.com-tahoe_speedstats_delay_rtt.html delay*RTT graph] shows this per-file delay as a multiple of the average round-trip
 time between the client node and the testnet. Much of the work done to upload