In People Maintenance there are 2 important fields:
With this field ticked, the name will appear in the PO Approvers dropdown list in Enter Purchase Orders.
The value in this field is the limit for PO approval by this person. When selecting a PO Approver from the dropdown list, the value of the total PO will be checked against the selected Approver's Approval Limit. If the PO value exceeds the limit, a warning will be displayed and another Approver will need to be selected. The allowable approvers list will redisplay listing only those Approvers who qualify to approve this PO