altos: Add easy mini plotting helper in test code

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/src/test/plotem b/src/test/plotem
new file mode 100755 (executable)
index 0000000..8bc392c
--- /dev/null
+++ b/src/test/plotem
@@ -0,0 +1,10 @@
+gnuplot -persist << EOF
+set ylabel "altitude (m)"
+set y2label "error"
+set xlabel "time (s)"
+set xtics border out nomirror
+set ytics border out nomirror
+set y2tics border out nomirror
+plot "$1" using 1:3 with lines axes x1y1 title "raw height",\
+"$1" using 1:21 with lines axes x1y2 title "error"
+EOF