diff --git a/services/render.py b/services/render.py
index 217965a..2cb017d 100644
--- a/services/render.py
+++ b/services/render.py
@@ -11,7 +11,7 @@ async def render_ammeter_chart():
 
     out = "data/ammeter.png"
 
-    time_range = f"{time.strftime("%Y-%m-%d %H:%M", time.localtime(times[0] / 1000))} ～ {time.strftime("%Y-%m-%d %H:%M", time.localtime(times[-1] / 1000))}"
+    time_range = f'{time.strftime("%Y-%m-%d %H:%M", time.localtime(times[0] / 1000))} ～ {time.strftime("%Y-%m-%d %H:%M", time.localtime(times[-1] / 1000))}'
 
     plot_line(
         times=[time.strftime("%H:%M", time.localtime(t / 1000)) for t in times],
@@ -32,7 +32,7 @@ async def render_water_chart():
 
     out = "data/water.png"
 
-    time_range = f"{time.strftime("%Y-%m-%d %H:%M", time.localtime(times[0] / 1000))} ～ {time.strftime("%Y-%m-%d %H:%M", time.localtime(times[-1] / 1000))}"
+    time_range = f'{time.strftime("%Y-%m-%d %H:%M", time.localtime(times[0] / 1000))} ～ {time.strftime("%Y-%m-%d %H:%M", time.localtime(times[-1] / 1000))}'
 
     plot_line(
         times=[time.strftime("%H:%M", time.localtime(t / 1000)) for t in times],