Quoting from docs.phuture
Bands are split into upper and lower bounds. Upper and lower bounds exist above and below the intended weight for an asset. The bands are always centred to the intended weight of each asset on the platform. Therefore, rebalancing bands comprise four key points. In the context of rebalancing bands lower and upper are adjectives to describe the distance away from the intended weight rather than the direction of the weight change. Let’s take a look at the key points above the intended weight. Let’s assign the variable WWWas the intended weight. The above lower bound, ALBALBALB, would be equal to W∗(1+x)W*(1+x)W∗(1+x), where xxx is a configurable parameter that defines the percentage increase in weight from the intended weight. The above upper bound, AUBAUBAUB, can be defined by W∗(1+y)W*(1+y)W∗(1+y), where yyy is a configurable parameter that delineates the percentage increase in weight from the intended weight and which satisfies the inequality y>xy>xy>x. Thus, if we use NWNWNW for new weight, when NW>WNW>WNW>W and ALB<NW<AUBALB<NW<AUBALB<NW<AUBthen NWNWNW sits in the interior of the rebalancing band and can trigger a rebalance. This process can be reversed to find the rebalancing band points below the intended weight.