Extract numbers from a text/log file, then use the details to draw up a graph! :(

 Hi guys,

Really sorry if this has been discussed before. I am using Sense, which is the Open University offline version of ScratchED. There has just been one drawback with the course which I couldnt stand! The instructions given to make programs get more and more vague to the point where it is incomprehensable! :(  As you can see:

 - Your chart will plot a maximum of 100 records.

.- The vertical axis of the chart will represent pressure. You should use an adequate vertical scale to make changes in pressure clear - (How can you manipulate a stream of data from a log file and append it on the stage to draw a graph?) 

- Plotting will begin at 100 units (y = 100). Lower pressures should be plotted below this level; higher pressures should be plotted above this level. Pressure readings will range from 0 to 120 units. - [ what does this even mean!? :(  ]

- The change in pressure values will come from the list holding values from the steam generator.

- The Stage should be cleared before each chart is drawn.

Can anyone please help me? I can provide more details if you private message me