weewx charts don't refresh without shift+refresh

[John Pierce]

I'm running weewx on a raspberry pi3b with raspbian, everything is as up to date as apt-get will get it...

weewx is rsynching the files to a debian based VPS running an Apache web server, https://freescruz.com/weewx/ 

the pi and the VPS and my Windows PC are NTP time synched.

I'm running Chrome latest on win10 latested, when I hit F5 or click on the reload button, the text all updates, but the graphs don't update unless i force it with SHIFT+refresh.    Do I need to change some setting or another ?

oh, hmmm, was running weewx 3.9.2, and I see raspian is offering me 4.1.1, guess I've been neglecting this .... ok, updated, merged my changes into weewx (mysql database on another box, basically, plus site info, and I added a few entries to the standard skin showing 24, 48, 72 hour rain totals

ok, phew, lost my customized rain fields, oh well, but 4.1.1 is working now, and has the same problem, a simple refresh doesn't update the graphs, I have to do a shift-refresh.

is this a quirk in Chrome, or a quirk in how my webserver is setup, or what?)

[John Pierce]

I'm running Chrome latest on win10 latested, when I hit F5 or click on the reload button, the text all updates, but the graphs don't update unless i force it with SHIFT+refresh.    Do I need to change some setting or another ?

ok, i added a Cache-Control directive to my .htaccess, and that seems to have fixed it.

<filesMatch ".(png)$">

    Header set Cache-Control "max-age=60, public"

</filesMatch>

(60 seconds because I'm updating every 120...)