Why the Lookback Period Matters for New Highs and Lows
Learn why a new high or low depends on the price measure and comparison period. Examine how old prices rolling out of the window affect thresholds and why confirming turning points takes time.
A new high or low means the current value has exceeded the maximum or fallen below the minimum over a specified comparison period. The same day's classification can differ depending on whether you use intraday or closing prices and the entire listing history or a recent window. Do not treat a price record and an improvement in company value as the same fact.
Specify exactly what has reached a high
The phrase new high often omits the comparison period and type of price. The highest close over the past month and the highest intraday price since listing are different conditions. Adjustments for splits or dividends can also change historical reference values. Check the scope of a reported high and use the same definition in your own notes. Rather than comparing against a maximum that includes today's high and then calling today a breakout, fix the reference value through yesterday first so it is clear which number was exceeded.
Distinguish the size of the record from the path taken
Barely exceeding a previous high and moving far beyond it to remain in a new range both set records, but their paths differ. Record the percentage exceeded, the closing position, and the position at the next observation separately for a more specific account. If highs rise but lows also fall, the pattern may reflect an expanding trading range rather than a strengthening directional trend. Conversely, rising lows without a new high may indicate a contracting range. Examining both dimensions prevents the single phrase new high from standing in for all the information.
Check for distortions from a rolling comparison window
The highest value over a recent period can fall even without a rise in new prices when an older high rolls out of the window. This is why crossing a new threshold alone does not establish a major trend change. A swing high also differs from the highest price in a period. Many methods confirm a swing high only after observing subsequent price declines, so retroactively claiming it was known that day introduces a timing error. Saving the reference values available on each date lets you check these effects directly.
Worked example
Hypothetical example: Suppose the highest price over the past 20 trading days through yesterday was 12,000 won, but that value rolls out of today's comparison window, leaving a high of 11,500 won for the preceding 19 days. Today's high of 11,600 won is a record in the new window, but it remains approximately 3.33% below yesterday's threshold of 12,000 won. Record the window's movement separately from today's price rise. If the close is 11,300 won, also distinguish the new intraday high from the closing-price result.
What to check
- Specify the lookback period and whether a new high uses intraday or closing prices.
- Save the prior reference value excluding the current candle.
- Examine changes in lows as well as highs.
- Check whether the threshold changed because an old value left the window.
Sources and primary materials
This is educational material about research methods. For an actual company decision, verify the filings and primary sources for the relevant period.