Marco Russo and Alberto Ferrari want to see zeroes in specific circumstances:
What makes this specific product interesting is that the product had sales in 2007, no sales in 2008 and it started selling again in 2009. Its behavior is different than the other products. Indeed, for most of these products one can argue that they start to produce sales when they were introduced in the market. Their behavior is quite intuitive: no sales up to a given point in time, then they start selling. We want to highlight this specific product because it shows a gap in sales when it was already present on the market. For other products, we are happy to blank them until their first sale. By doing this, we show gaps when they are real, and we avoid showing non-relevant information, that is products that could not produce sales because they were not even available to sell.
Read on to see how they do this.