Hi Rob,
The contrast control shown in that tutorial is from an older version of Photoshop. The newer versions have a choice of using "Legacy". If you check the "Use Legacy" box, your contrast control will go from -100 to +100 otherwise from -50 to +100. Using the Legacy option applies contrast the old way and can cause clipping or loss of image detail. However, it can be useful for editing masks or scientific imagery. Click the link below to read about it.
Click HereHope this is helpful.
P.S. I really think the Legacy option is there mostly for backward compatibility reasons. That is, for editing the brightness or contrast of images created with older versions of Photoshop.