[rrd-users] Sum of diff's

[Leif Neland]

Every hour I record the number of items left for sale of something.
Once in a while, the stock gets filled.
I want to graph the sale every day. I obviously miss the sale during the 
hour, where the stock gets filled, but that can't be helped; I don't know 
how much is added to the stock.

CDEF:sale=PREV(stock),stock,-,0,MAX

Eg for each hour at the day, I have this:
Stock    Computed Sale
14        NaN
12        2
12        0
9           3
29        0        <- here at least 20 items are added to the stock
...
7        ..

So the total sale for this day is 27; I want only one point in the graph for 
this.
I only have hourly resolution for one week, so I somehow must have entered 
this value 27, when the data gets consolidated for only datapoint per day. 
If not, I will get registered a sale of 7, and the addition of 20 is lost.

Can this be done? Or must I each night extract the last 24 values, compute 
the sale, and enter it into another rrd?

Leif









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