Trends using Counter as Log Type

[batistacaceres]

I have an object that increse its value each 15 min by 10: Example
Time    Value
00:00  -  0
00:15  -  10
00:30  - 20
00:45  - 30
01:00  - 40
00:15  - 50
00:30  - 60
00:45  - 70
02:00  - 80
.. and so on

Then, I have created a trend with that object, using the following parameters...
Log type: Counter
Agregate function: Last value
Trend resolution: 1 hour

I expect the Graph show me the diference between  the value in current hour and the last hour, for example
Time    Value              Trend Result that I expect
00:00  0                      -- >>  0
00:15  10         
...
01:00  40                    -- >> 40
00:15  50
...
02:00  80                    -- >> 40
00:15  50
.. and so on

but It always shows me cero values. Am I missunderstanding something??. What am I miss understanding about counter Log Type, or about the Agregate function???
What I want to do is, to graph (Trends) the diference in values between current hour and the last hour. Please could you help me??
I need to understand well How parameters "Log Type" and "Agregate function" work in the trend?? Is there a little documentation about it??

thank you very much
best regards

[admin]

You are probably running an older firmware. Aggregate function has been disabled for Counter type as any other mode than Average produces incorrect results. Aggregate function should only be used with Absolute value log type.

[batistacaceres]

Thank you very much, I have updated to the last firmware and now it is working very well, thank you.

best regards