In card counting, what exactly do index numbers mean?

I have read about the Illustrious 18, and understand that if the true count is at or above the index number, that you should deviate from basic strategy. This is what I am confused about: What about the indexes that are negative? Example: 13 vs. 3 has an index of -2. Does that mean that if the running count is higher (more positive) that I should still hit on that? Or only if it is lower (more negative)?

 
 
 
 
 
 
 
 
 
 
 
 

With the increasing cost of gas, does this mean that casinos are going to tighten up their slot machines,..?

And other games there to offset their decreased ability to save money given how those casino employees and managers also automobiles and the cost of gas is hurting them to?

So because of higher gas prices, how much tighter are they planning to make their machines?
If they make their machines tighter, I am going to b#tch to the gaming commission like there is no tomorrow.