Because the US stock market only has 6 and a half hours per trading day, 9:30AM EST ~ 4:00PM EST, that is, 390 minutes. Therefore, we should accurately look at the changes in the medium-term K-line. We should not use the 1-hour K-line, but the 65-minute K-line, because 390 / 6 = 65M, 6 K-lines a day, so that the trading volume and other data are accurate. That is to say: 1H -> 65M 4H -> 195M 8H/12H/1D -> 390M