Understanding normal probability plots I am a teacher that will be teaching about Normal Probability Plots.
This topic is new to me and I would be grateful for any help.
Essentially the specification for the course expects students to identify normality with how straight the line is and nothing else but I'd like to understand further.
Here is a question from a sample paper (I hope it is visible).  I have  a few questions.

1) What are the axes labels?  I have tried background research and I've seen different versions but none like this.
2) How is it calculated and drawn?  I'd appreciate a basic explanation.  I have an underlying belief it has something to do with $Z=\frac{X-\mu}{\sigma}$ being a straight line for fixed $\mu$ and $\sigma$ but the various types of diagrams is sending me in circles.
I know about the Normal distribution at least as far as the basics.
Thanks for any help.  Please forgive if this is a repetition (I did try to search but questions were more complex than I require)
Edit
I have found how it was plotted but would still like to understand why the straight line shows normality.
Edit2
If I used the CDF for a different distribution (Poisson) would a straight line show a poisson dist?
Edit3 
I think I understand now and will put a worked example as an answer when I've chance (might be a day or two).  
 A: Here is a worked version of my problem.  
The data is made up but I hope to have answered my question.
We can create a table of percentiles.  We assume that the 3rd data value will have $38\%$ less than or equal to it.
$$\begin{array}{c|c}x&25&32&41&52&62&71&80&81 \\ \hline \text{Position when ordered}&1&2&3&4&5&6&7&8 \\ \hline \text{Percent}\le \text{Position }&13&25&38&50&63&75&88&100\end{array}$$
There is no greatest value for the Normal Distribution so using the percentages as it fails.  
We can get around this by taking the midpoints of the percentages.
$$\begin{array}{c|c}x&25&32&41&52&62&71&80&81 \\ \hline \text{Position when ordered}&1&2&3&4&5&6&7&8 \\ \hline \text{Midpoint of Percent}&6&19&31&44&56&69&81&94\end{array}$$
We now  find the $z$ such that $P(Z\le z)=\text{Midpoint of Percentage}$
$$\begin{array}{c|c}x&25&32&41&52&62&71&80&81 \\ \hline  \text{Midpoint of Percent}&6&19&31&44&56&69&81&94 \\ \hline P(Z \le z)=\text{Midpoint of Percentage} &-1.53&-0.89&-0.49&-0.16&0.16&0.49&0.89&1.53 \end{array}$$
The Normal Percentage Plot now graphs $(x,z)$
Now $\mu=55.5$ and $\sigma=20.12$ so we can graph the straight line $z=\frac{x-\mu}{\sigma}$.
If the plot of $(x,y)$ resembles the line of $z=\frac{x-\mu}{\sigma}$ then the data is looking likely to be Normal.  
Is this correct?  If this needs adding to the question I will do so.  If alterations are necessary I'd be grateful for any adjustments.
I have a slight doubt about assuming $38\% \le \text{3rd position}$.  In particular I see this is fine when trying to used the CDF of the normal distribution as it is symmetrical but don't see how it can be adapted to test for other potentially non symmetrical distributions such as Poisson.
I have tried to express my understanding as best as I could and apologise if it is garbled. 
