High, mid, low reference level calculation

Hi,
    Does anyone know the equations for calculating the high, mid, low reference voltage?    I have set the reference voltages to 10%, 50% and 90%. I just don't know based on what the digitizer calculates the level.    For example 1, the Mid level is calculated as (Vtop+Vbase)*0.5. Should it be (Vtop-Vbase)*0.5?   The Hi and low reference calculations also do not add up. I was using a signal generator to generate the signals.
I am using PXI-5224 and niScope.lib verison 3.5.
Example 1
3Mhz Square Wave 3.3VPP
ch0                              ch1
Vpp=4.704506            Vpp=4.575151
Vtop=3.304177           Vtop=3.304474
Vbase=-0.003679       Vbase=-0.618361
VHigh=3.304177          VHigh=3.304474
VLow=-0.003679        VLow=-0.001788
VMax=4.011691           VMax=3.956790
VMin=-0.692815           VMin=-0.618361
LowRef =0.327107 V    LowRef =-0.226078 V
MidRef =1.650249 V     MidRef =1.343056 V
HiRef =2.973391 V        HiRef =2.912190 V
RiseTime =7.437264      RiseTime =141.967975
FallTime =7.438606       FallTime =9.800559
Example 2
ch0                                 ch1
Vpp=4.612737               Vpp=4.580664
Vtop=3.295510             Vtop=3.311956
Vbase=-0.001876         Vbase=-0.016182
VHigh=3.295510          VHigh=3.311956
VLow=-0.001876          VLow=-0.016182
VMax=3.971204            VMax=3.965059
VMin=-0.641533            VMin=-0.615605
LowRef =0.327863 V    LowRef =0.316632 V
MidRef =1.646817 V      MidRef =1.647887 V
HiRef =2.965772 V        HiRef =2.979142 V
RiseTime =7.605729     RiseTime =7.745428
FallTime =7.536156       FallTime =7.708538
Message Edited by kkwong on 04-16-2009 03:56 AM
Solved!
Go to Solution.

Hi all,
I think I messed up the calcuation. The reference voltages are are correct. It is the (Vop+Vbase)/2 for mid ref level. The Lo and hi are also correct.

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