Gui script help

these are the consts

private const int offSet = 5;

private const int Line_Height = 20;

private const int Stat_Label_Width = 100;

private const int Base_Label_Width = 30;

private const int Button_Width = 20;

private const int Button_Height = 20;

private int statStartingPos = 40;

This is what i'd like to change into a HorizontallSlider

How would i implement a slider instead of a button to change the values ?

     if(GUI.Button(new Rect(offSet + Stat_Label_Width + Base_Label_Width, statStartingPos + (cnt * Button_Height), Button_Width, Button_Height), "-")) {
         if(_toon.GetPrimaryAttribute(cnt).BaseValue > Min_Starting_Attribute_Value) {
             _toon.GetPrimaryAttribute(cnt).BaseValue--;
             pointsLeft++;
             _toon.StatUpdate();

Any help would be great i apologize for posting a lot of scripting questions but how else am i mean't to learn

MellowNinja