Inertia
A smoothed version of the Relative Volatility Index, fitted with a linear regression, meant to show whether a trend has enough underlying “inertia” to keep going.
What the numbers mean
Two settings: the Relative Volatility Index period, and the number of bars in the linear regression that smooths it. Donald Dorsey built Inertia by running his own Relative Volatility Index through a regression line, which turns a jumpy volatility reading into a slow trend state on a 0–100 scale. The input is the Relative Volatility Index — not the similarly abbreviated Relative Vigor Index.
- 14 — the Relative Volatility Index period underneath it
- 20 — the number of bars in the linear regression that smooths it
- 50 — the dividing line between upward and downward inertia
How it is used
Read as a directional state rather than a trigger: above 50 the trend is considered to have upward inertia, below 50 downward, and traders use it to decide which side to take signals from.
- Above 50 → the trend is considered to have upward inertia
- Below 50 → downward
- Used to decide which side to take signals from, not when to take them
How it relates to everything else
Inertia converts an oscillator into a slow regime filter, which puts it in the same job as ADX or a 200-day average: it tells you which direction to trade, while faster tools decide the moment.
- Built from the Relative Volatility Index — not the Relative Vigor Index, despite the shared abbreviation
- Regime filter, like ADX or a 200 SMA
- Too slow for timing by design
What to watch for
Heavy smoothing makes it very slow to change state — useful as a background filter, useless for timing.