diff --git a/README.md b/README.md
index fca70a7..d4ad963 100644
--- a/README.md
+++ b/README.md
@@ -189,6 +189,25 @@ The rule: find the drives' normal peak, put `DISK_RAMP_LOW_OFFSET` a couple of d
 above it, and let the alarm (`DISK_ALARM_OFFSET`, 5c below the limit) catch anything real.
 Cooling a healthy drive from 57c to 53c is not worth 27% more fan.
 
+### Let Dell do the CPU; the disks are what it cannot see
+
+Dell's profile has the chassis thermal model and is good at CPU cooling. What it does not
+do is look at drive temperature *at all*. So the CPU curve should approximate Dell's
+rather than out-bid it, and the disk curve is where this script earns its keep.
+
+Measured on `iz-pve0` under a sustained migration, with the service stopped so Dell had
+control: Dell held **5880-6120 RPM with CPU2 at 70-74c** — 3c below its own 77c warning
+point. An earlier CPU ramp of 62-73c asked for 36-50% across that same range, i.e. up to
+**9720 RPM against Dell's 5880**, while the drives ran 2c *warmer*. The extra 3800 RPM
+bought nothing.
+
+The fix was to keep the CPU ramp out of the way until 75c and reach full speed exactly at
+77c, where iDRAC itself starts warning. Result: 26% / 5880 RPM for 50 of 60 samples,
+matching stock, with brief excursions to 35% when CPU2 touched 76c.
+
+Calibrating the CPU ramp against an *idle* reading is what caused this. Idle tells you
+where the floor should be; only a loaded CPU tells you where the ramp should start.
+
 ### Expect to run above stock on some hosts, legitimately
 
 Dell's profile does not look at drive temperature at all — only CPU, inlet and exhaust.