Google Trends - How Much Search Volume
Have Certain Keywords Gotten Over Time?

Google Trends - If you want to see a nice line graph of how the search volume of two or more keywords did over a certain period of time, then use Google Trends. You can select a time period and a region. You can try using this to see if there is an upward or downward trend in your market. The example I used was for Pepsi vs. Coke.