Explain residual panel of calibcant bump figure..

diff --git a/posts/calibcant.mdwn_itex b/posts/calibcant.mdwn_itex
index 05581d6b1261b7959421135d8f4c66ea2f16e7f4..9844bc4c0c97dd5dfc74b5dea27ae69aec93ca8e 100644 (file)
--- a/posts/calibcant.mdwn_itex
+++ b/posts/calibcant.mdwn_itex
@@ -42,7 +42,9 @@ The contact region of surface bumps can be fit with either linear or
 quadratic models.  Here is an example of a single surface bump fit
 with a quadratic model.  The green line is the initial guess (before
 fitting), the red line is the final model (after fitting), and the
-blue dots are measured data points.
+blue dots are measured data points.  The red dots in the bottom panel
+are the residual, which looks cubic because we've subtracted a
+quadratic model.
 
 [[!img bump.png alt="Surface bump for photodiode sensitivity"
   title="Surface bump for photodiode sensitivity" ]]