How did movie studios learn a movie was a hit through rentals?

In "Tremors: Making Perfection", one of the new documentaries on the recent Arrow release of the 1990 film Tremors, several of those interviewed mention how delighted they were when the movie became a cult favorite as a VHS rental after more or less flopping at the box office.

But how was this measured? I presume that a popular VHS rental would require the stores to order more copies in order to serve more customers at once, plus the wear and tear through increased rentals would also require the replacement of "retired" tapes. But to me that would seem to be an unreliable metric at best.

One of the references on the movie's Wikipedia page links to this article from the Los Angeles Times, its relevant part reads:

Right now the rental Top 20 is unusually heavy with dramas and dark comedies with adult appeal. That largely explains why many renters -- teens in particular -- are flocking to “Tremors,” the comedy/horror flick which shot up to No. 10 in just two weeks.

This mention of a "rental Top 20" suggests that some kind of organization kept tabs of such things. I assume a company would poll a representative sample of shops (a mix of big chains and mom and pop stores). Does anyone know what the exact methodology was?