MSO58 VRMS Measurement

I am trying to measure Vrms of a signal on a MSO58-Oscilloscope. I am trying to measure the ripple voltage of a signal. The Oscilloscope has multiple ways to measure Vrms, each of which show a different value. I would like to know why that is.
The DPM-Measurement also depends on the selected Frequency. Why is that, what is the formula for calculating the ripple? 

the measurement algorithms are described in the Help-Manual, in the section "Measurement algorithms".
4, 5, 6 Series MSO Help | Tektronix
I'll send you an e-mail with details

Thank you. I am still unsure though what exactly The "Ripple Frequency" parameter does for DPM-measurements. The values also seem to depend on the horizontal time scale.

let's follow up via e-mail.
I sent you one on 26/03