The Rydex Assets Ratio is a market sentiment indicator based on the flow of money in and out of bullish and bearish mutual funds. I believe the original indicator was based on just two funds in the Rydex family, the Nova fund which was bullish, and the Ursa fund which was bearish. By dividing the assets in the Nova fund by the Ursa assets you had a ratio, and an indicator.
The range of funds grew and a variety of ratios have been created over the years. I use my own choice of funds, hence “my version” of the ratio. Great thing is the data is readily available and can be collected on a daily basis here:
https://www.guggenheiminvestments.com/mutual-funds/navs-assets
The indicator (like most sentiment indicators) is most useful at extremes and is interpreted in a contrarian fashion, i.e. an extreme low ratio will often occur at, or close to a low in the market. However, unlike a lot of other sentiment measures, this one often gives reliable indications of a market that has got too speculative and is close to a top of some degree.