Author's Note: This is an interesting technique but I believe a simpler and more general purpose method is in a blog post from Aug 2016. Search on "QlikView Maven Is My KPI Getting Worse or Getting Better"
I did a weekend project several weeks ago where I was working with a database containing some business measurements taken each day over a long stretch of time. I wanted an easy way to visualize whether the aggregate measurements were getting better or worse over time. In order to satisfy the “easy” part of that objective, I decided to build expressions that would automatically split the available measurement dates into two groups: the earliest half of the dates and the latest half of the dates. That would allow me to create charts with a heat map feature that easily identifies areas for further investigation.