diff --git a/GNUmakefile b/GNUmakefile
index 573253b..a20fe79 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -1,2 +1,5 @@
 CFLAGS = -std=c11 -Wall -ftrapv
 all: timezone-history
+
+%.png: %
+	tsplot --time_t --finalresolution 300  $^ > $@