Outside bar

Marks a minute whose high and low both extend past the previous minute's range.

The indicator marks each one-minute bar whose high is above the previous bar's high and whose low is below the previous bar's low. In other words, the current bar's range fully contains the bar before it. It does not look at the close or at whether the bar is up or down, so it describes range expansion, not direction.

How to read it

Each marker sits on the candle that engulfed the previous candle's range.
A marker says the minute was wider than the one before on both sides, not which way price moved.
Expect markers to cluster in choppy stretches, and check the next few candles for direction.

What it outputs

Outside bar: Marks each one-minute bar whose range fully contains the previous bar's range. The close does not decide it.

When it fires

Fires on a bar whose high is strictly above the prior bar's high and whose low is strictly below the prior bar's low. That moment means the minute's range widened on both sides, a sign of volatility or indecision, with no direction attached.

Pitfalls

Direction is ignored: a bar that closes at its low and one that closes at its high both mark. Do not read a marker as bullish or bearish on its own.
On one-minute bars it is busy, not rare: about 80 markers a day and roughly one bar in 12 on the SPY sample for September 2026. The name comes from daily-bar charting, so this is a different, much noisier signal.
Both comparisons are strict, so a bar whose high or low only matches the previous bar does not mark.