What is a positive and negative value for M in the formula y equals Mx plus B?

The formula y=Mx + B is the slope intercept equation of a line. If you where to graph this on a 2 dimensional graph with x and y axes the number represented by M would be the slope of the line. A positive value of M would mean a positive slope and the line will rise as one views it from left to right. A negative value of M would indicate a negative slope and the line will descend as one views it from left to right. A value of zero for M would indicate a horizontal line.