I would like to collect accumulated statistics over several days, but the router seems to be resetting the counters to zero every 24hours or so.
I cannot find how (if) I can turn that off so the counters keep going.
Alternatively, one can go for a 64-bit counter implmentation so the counter can last much longer before it resets to 0.
The bytes count on the statistics page is a 32-bit counter that rolls back to 0 when the count reaches 2^32 bytes. You might need to take samples of this counter hourly and use a graphing software to take this discontinuity into account.