NI 4070 Digital Multimeter Accuracy

[RGranados]

Hello, I have a doubt about the accuracy of this digital multimeter. From this link I see that for measuring frequency the accuracy is totally related to the accuracy of the time base clock (25ppm) and also you need a good voltage and free noise signal to avoid other errors. But we will suppose no noise and correct amplitude of the signal. So from this I conclude that accuracy depends only from time base accuracy.

Reading more, from the description of how this digital multimeter measures the frequency "The NI 4070/4071/4072 measures frequency by counting the number of zero-crossing rising edges of the input signal, using an onboard 28.8 MHz timebase." I know that an error from measurement of +/- 1 count of the time base cycle will happen, because the signals are not in phase. ( See Method 1 here)

Is this true for the 4070 and it is not said in the specifications?. Or it does other type of measurement eliminating this error? If not, for a complete accuracy I should have Total Error = Clock error + Measurement error? Beign Measurement error the one stated in the second link in Method 1?

Thank you. If you need that I develop more the question please tell me. 

[CodeMonster]

In the following document you can read the specifications of the PXI-4070

http://www.ni.com/pdf/manuals/371304j.pdf

In the page number 8 you can see the percentage that you mention and its already the Total Error that you mention.

Only be carful with the range of V that you use to fulfull the Hysteresis (http://zone.ni.com/reference/en-XX/help/370384N-01/dmm/measuring_frequency2/)

[RGranados]

Thank you, for your answer but I still don't understand the specifications. It says "2-Year Accuracy 0 °C to 55 °C ± % of reading"  this has a value of 0.01,  and the % of reading is the 25ppm. What is the meaning of the 0.01? And does this means the accuracy is 0.01 +/- 25ppm? 

Sorry, to insist. But it is not clear to me.

Thank you again.