Hi,
I tried to use Visualization → Legend → Value total but i got right values only for no more then 2 day.
I am not sure if it problem of PromQL, Grafana ot smt else.
I have attached screenshot with Total column.
Prom expr: sum(rate(nginx_ingress_controller_response_size_sum{ingress!=“”}[2m]))
Grafana v6.3.5