diff --git a/garlic/doc/Makefile b/garlic/doc/Makefile
index d6f72f9..f2ecc0a 100644
--- a/garlic/doc/Makefile
+++ b/garlic/doc/Makefile
@@ -1,10 +1,14 @@
 all: execution.pdf execution.utf8 execution.ascii pp.pdf pp.utf8 pp.ascii\
-	branch.pdf
+	branch.pdf blackbox.pdf
 
 TTYOPT=-rPO=4m -rLL=72m
 PDFOPT=-dpaper=a4 -rPO=4c -rLL=13c
 PREPROC=-k -t -p -R
 
+blackbox.pdf: blackbox.ms Makefile
+	REFER=ref.i groff -ms $(PREPROC) -dpaper=a4 -rPO=2c -rLL=17c -Tpdf $< > $@
+	-killall -HUP mupdf
+
 %.pdf: %.ms Makefile
 	REFER=ref.i groff -ms $(PREPROC) $(PDFOPT) -Tpdf $< > $@
 	-killall -HUP mupdf
diff --git a/garlic/doc/blackbox.ms b/garlic/doc/blackbox.ms
new file mode 100644
index 0000000..313a0f5
--- /dev/null
+++ b/garlic/doc/blackbox.ms
@@ -0,0 +1,40 @@
+.\" Use helvetica family
+.fam H
+.PS
+moveht=0.1
+boxwid=1
+sht=boxht + 0.1
+hspace = boxwid + 0.2
+right
+G: [
+  boxwid=1
+  extrawid=1.8
+  right
+  A: box "nix"; arrow;
+  B1: box wid extrawid "App source code" "PM branch, defines...";
+  move to (A.sw.x, A.y - boxht - moveht)
+  A: box "garlic/nix"; arrow;
+  B2: box wid extrawid "App run config" "Input size, algorithm...";
+  move to (A.sw.x, A.y - boxht - moveht)
+  A: box "garlic/nix"; arrow;
+  B3: box wid extrawid "Build config" "MPI impl, O3, CC version...";
+  move to (A.sw.x, A.y - boxht - moveht)
+  A: box "garlic/nix"; arrow;
+  B4: box wid extrawid "Run config" "Nodes, affinity";
+  move to (A.sw.x, A.y - boxht - moveht)
+  A: box "MN4"; arrow;
+  B5: box wid extrawid "Hardware" "Cache size, intercomm...";
+]
+movewid=1
+move
+circlerad=0.4
+E: circle "Execution"
+arrow
+box "Result"
+rspline = 0.5
+arrow from G.B1.e to E chop 0 chop circlerad
+arrow from G.B2.e to E chop 0 chop circlerad
+arrow from G.B3.e to E chop 0 chop circlerad
+arrow from G.B4.e to E chop 0 chop circlerad
+arrow from G.B5.e to E chop 0 chop circlerad
+.PE