Slow site performance when mean dose per week plots used

[David Platten]

This seems to particularly affect the radiographic plot. It may be due to the way that the queryset is being accessed. The information here may be of help: https://docs.djangoproject.com/en/1.7/topics/db/queries/#caching-and-querysets

[David Platten]

I have added the ability for the user to change the time period that is used to calculate each data point (a99dfb3). The user can also switch off these plots (221a592, 8b9b604). I think this is now resolved.