Interpolated data?

[patricktokeeffe]

I see plotted data that appears to be interpolated, but don't understand why. The dynamic interval hasn't been changed (1 = 10 seconds) and my source data is updated approximately 10-15 seconds after the start of each minute.

My data value changes from 4 → -99 but the plot shows an intermediate value of -32.195. Where does this nonlinear transition come from?

[XavierBerger]

You should find your answer in RRD documentation.
This database is doing some average that might explain what you saw.