hi, i have got a very long text (and graphics)  that I would like to draw to the screen. I would like to draw it bit by bit, so that only ever 7 words of the text are seen on the screen. I am using a slider to move the elements on and off the screen. So when I am calling my classes in draw() I would like the slider value to determine whether i am loading elements 0-6, 1-7, 2-8, 3-9... and so on.
My lowest slider value is 0 and the highest 600.  When the slidervalue has gone up +3.0 to the previous value or gone down -3.0 to the previous value I want to change which words are shown. Below is an outline of my sketch. I am struggling to figure out, how i can make this work for all values between 0 and 600 and how I would figure out if the value has increased or decreased.

int sliderController = 0;
ControlP5 controlP5;
Slider s;
float yPos = 0 ;
Rect2Gram[] rects2Gram;


void setup()
{
size(screen.width,screen.height-100);
 frameRate(25);
 background(backGroundCoLour);
 smooth();
controlP5 = new ControlP5(this);
Slider s = controlP5.addSlider("mySlider", 0, 600, 20 , width - 15, marginY , 5  , height - (marginY)-80);
s.setId(21);
}


void draw()
 {  
  //how do I amend this to work for all values between 0 and 600
 // to add 1 to sliderController if yPos increases by 3
// or to minus 1 off sliderController if yPos decreases by 3
   if ( (yPos >=3.0) && (yPos <=6.0))
  {
     println( "yPos: " + yPos);
     sliderController = 1;    
     println( "sliderController: " + sliderController);
     
  }
     rects2Gram = new Rect2Gram[7];
     for (int i = sliderController; i < sliderController + 6; i++)
     {  
        rects2Gram[i] = new Rect2Gram (words.length, words, i, words[i], yPos,);
        rects2Gram[i].createTwoCombinations();
         
     }
 }

void controlEvent(ControlEvent theEvent)
{
 if( theEvent.controller().id() == 21)
  {
       yPos = theEvent.controller().value();
  }

I am loading my Rect2Gram class for words in stories of different length. For each word the class is loaded and some graphics are drawn. map() sounds great for generating the slidervalues in accordance to how many words each story has. But it doesn't tell me yet whether the slidervalue has increased or decreased from the value it previously had. how would i do that?
yPos moves the y position of the graphic for each word. When the user moves the slider some words are moved off the screen and others come onto it. Because my stories are very long i thought the slidervalue could also control which words in my word[] i am drawing. word[0] to word[6], word[1] to word[7]. Is that possible?

sorry, i am being really slow, just can't get into my head how the variable would be able to know in which direction it has changed. if i set something like this

int sliderController = 0;

up before setup() what to i need to do in draw() to recognize the change?