The approval rule threshold field sets the value of an order that triggers the approval rule. Orders that have a value equal to or above the threshold will need to be approved by the number of users set in the approval rule.
There is no upper threshold set for an approval rule. An approval rule will apply to all orders equal to or above the value set in its threshold unless there is another rule with a higher threshold related to the same department. For orders equal to or above the value of the higher threshold they will follow the approval requirements set in this rule.