Help with understanding definitons for qPCR

[newbie17425]

Hello,

 

I recently did a qPCR (just a trial) using a ABI stepone plus system and i am stuck with the results. I am unable to understand the following:

 

1) Ct Mean: I have only one Ct value for a sample but it gives me a mean Ct mean value. How?

Even some samples went undetermined but it still shows a Ct mean value. Why?

 

2) What is meant by quantity and why is that empty?

 

3) What is Ct Threshold?

 

4) I have three Tm values. I assume that is the melting temp. of the primers. Am i correct? Why are there 3 Tm values?

 

Please find attached a screenshot of the result

 

Thanks