Big Business provides options for showing Line Numbers on screen for reference.  
When this option is turned on, you can click on the Number to see options such as:
  Add Row Above
  Add Row Below
  Move To Row 1
Line Prefs control whether you see Line features like Line Numbers.
This Solution describes this setting.  (6627)
Line Numbers are now an option for transactions with Line Items:
  Quote, Order, Invoice
  Request, Purchase Order, Bill
  Item Adjustment, Warehouse Transfer
Line Numbers enable new features to:
  Show - click to show the Item
  Insert - click to add a row above or below
  Sort - use the Sort button even on saved transactions
  Reorder - click to Move To another row
This Solution describes this setting.  (6628)
PO Lines is a new option for Line Prefs to match line numbers from the PO to Bills.
When enabled this setting links items on the Bill to items on the PO and shows the Line Number from the PO in the PO # column on the Bill window.
Exports of POs and Bills are automatically updated to include PO Line #'s.
The Sort button for Line Items permanently sorts the contents of:
  Quote
  Order
  Invoice
  PO
  Bill
This Solution describes using this feature. (6500)
Big Business 14.70 fixes Line Numbers to show a Popup when clicked without focus.
Line Numbers are automatically added on Imports such as Quote, Order, and Invoice.
Updated imports include Bill Line Items, Invoice Line Items, Purchase Order Line Items, Quote Line Items, and Sales Order Line Items.