labview keithley 2635a output

[cq7]

I am working on a Labview program to control Keithley 2635A SMU and I am looking at sample Labview VIs on the website. I decided to use the configure source and meeasure rather than the advanced sweep. In this VI, there is a subVI "Keithley 2600 Series.lvlib:Sourcelimit.vi" that can be used to measure and output different functions: Current, Voltage, Resistance, IV, Power. I am particularly interested in IV however I want to make the program such that I can use all (and save the output and source and get a graph).  

However, I realized that the source input (level), I input into the program differs slightly from the V value in the IV function (differs at the 4th significant digit). I want to ask which gives a more accurate and more precise value, the V I input in my program or the V from the IV output for the IV graph.

I have these concerns because I am not sure:

1. If I use the V from IV output (which is a string output  which I can turn into number), then:
a.) Is it the same V that exactly corresponds to the I value recorded/measured? (and so more accurate?)
b.) Is it a V value whose number of SF has been limited by rounding it off and storing it as a string? I realized it is only 6 significant figures max.

2.If I use the V from my input (programming input):
a.) Is this V different from the actual V sourced by the instrument to the sample?
--> therefore, less accurate?
b.) But it does not undergo recording as string and being converted to another format (so no rounding off error)? --> therefore more precise?

Thank you very much and I will very much appreciate your answer.

[Salomon8]

Hey

I am thinking about using a keithly SMU in my next project. Until now I've only installed the driver and looked at the VI's

"A SMU is a precise power supply, which can supply and measure voltage up to a resultion of 1 mV."

http://www.ni.com/white-paper/6850/de

Setting your source input to a specific value will therefore not be totally precise. (only up to millivolt)

Thus I would recommend the first way you described since the data of your IV Graph is a measured one and therefore more precise.

One additional question:

How did you find out that voltage values only have 6 significant figures max? Can that be read from the VI???

I would be glad for a reply and look forward to discuss this topic a little further (If you want)

P.S Sourcelimit.vi" is not a VI to measure and output different functions, is it??? I just got a little confused by your post.