How do you measure the effectiveness of print media advertising?

Measuring the impact of advertising has been a top concern of advertisers for over100  years.
A now famous quote by John Wanamaker,* department store owner in the early  20th century, demonstrates this point: “Half the money I spend on advertising is wasted;  the trouble is I don’t know which half.” But still, effectiveness of Print Media advertising can be measured by offering some discount coupon in the advertisement, like if some one brings the cutting of the Ad he is entitled to get lets say5% discount, so by using the data onec can find ROI.
Also, you can follow the sales trends of your pre & post advertising to get some idea about ROI. 

A balance between selling price volume and quality.
Also a good pricing category (price list list)for government corporate and agencies.