Taken from Bisac X12 v3060
 Header Segments
| ST | Transaction Set Header | 
| BAK | Beginning Segment for Purchase Order Acknowledgement | 
| N1 | Name Segment | 
Detail Segments
| PO1 | Baseline Item Data | 
| CTP | Pricing Information | 
| ACK | Line Item Acknowledgement | 
Summary Segments
| NTE | Freeform Text | 
| CTT | Transaction Total | 
| SE | Transaction Set Trailer | 
ST Transaction Set Header
| Element | Name | Value | 
| ST | Segment Identifier | ST | 
| ST01 | Transaction Set ID | 850 | 
| ST02 | Transaction Set Control Number | Assigned by Sender (unique) | 
BAK Beginning Segment for Purchase Order Acknowledgement
| Element | Name | Value | 
| BAK | Segment Identifier | BAK | 
| BAK01 | Transaction Set Purpose Code | 00 = Original | 
| BAK02 | Acknowledgement Type Code | AC = Acknowledgement with detail and change | 
| BAK03 | PO Number | Identifying number for PO assigned by orderer/purchaser | 
| BAK04 | Date Ordered | YYMMDD | 
| BAK06 | Request Reference Number | Assigned by Sender (unique) (same as ST02) | 
| BAK09 | Current Date | YYMMDD | 
N1 Name Segment
| Element | Name | Value | 
| N1 | Segment Identifier | N1 | 
| N101 | Name Identifier | BS = Bill and Ship To | 
| N102 | Name | Full Text Name | 
| N103 | ID Code Qualifier | 15 = SAN | 
| N104 | SAN | SAN Number | 
PO1 Baseline Item Data
| Element | Name | Value | 
| PO1 | Segment Identifier | PO1 | 
| PO101 | Assigned Identification | Line Item Number | 
| PO102 | Quantity Ordered | Quantity Ordered | 
| PO103 | Unit of Measure Code | UN = Units | 
| PO104 | Unit Price | Price per Unit | 
| PO105 | Basis of Unit Price | SR = Retail/List/Suggested Selling Price | 
| PO106 | Product ID Qualifier | IB = ISBN | 
| PO107 | Product ID | ISBN# or Speedy# or EAN or UPC (Optional) | 
| PO108 | Product ID Qualifier | IB = ISBN VN = Vendor Number EN = EAN UP = UPC | 
| PO109 | Product ID | ISBN# or Speedy# or EAN or UPC (Optional) | 
| PO110 | Product ID Qualifier | IB = ISBN VN = Vendor Number EN = EAN UP = UPC | 
| PO111 | Product ID | ISBN# or Speedy# or EAN or UPC (Optional) | 
| PO112 | Product ID Qualifier | IB = ISBN VN = Vendor Number EN = EAN UP = UPC | 
| PO113 | Product ID | ISBN# or Speedy# or EAN or UPC (Optional) | 
| PO114 | Product ID Qualifier | IB = ISBN VN = Vendor Number EN = EAN UP = UPC | 
| PO115 | Product ID | ISBN# or Speedy# or EAN or UPC (Optional) | 
CTP Pricing Information
| Element | Name | Value | 
| CTP | Segment Identifier | CTP | 
| CTP02 | Price Identifier Code | SLP = Retail/List/Suggested Selling Price | 
| CTP03 | Unit Price | Retail Price (decimal included, i.e. 9.99) | 
| CTP04 | Quantity | Shipped Quantity | 
| CTP05 | Composite Unit of Measure | UN = Units EA = Eaches (Cases) | 
| CTP06 | Price Multiplier Quantifier | DIS = Discount Multiplier | 
| CTP07 | Multiplier | Discount Multiplier (discount of 20% would have .8 here) | 
ACK Line Item Acknowledgement
| Element | Name | Value | 
| ACK | Segment Identifier | ACK | 
| ACK01 | Line Item Status Code | AC = Item accepted and shipping (shipping) | 
| ACK02 | Shipped Quantity | |
| ACK03 | Unit or Basis for Measurement Code | UN = Units | 
| ACK04 | Date/Time Qualifier | 068 = Current Schedule to Ship | 
| ACK05 | Date | YYMMDD | 
| ACK07 | Product ID Qualifier | IB = ISBN | 
| ACK08 | Product ID | ISBN# or Vendor# or EAN or UPC | 
| ACK09 | Product ID Qualifier | IB = ISBN VN = Vendor Number EN = EAN UP = UPC | 
| ACK10 | Product ID | ISBN# or Vendor# or EAN or UPC | 
| ACK11 | Product ID Qualifier | IB = ISBN VN = Vendor Number EN = EAN UP = UPC | 
| ACK12 | Product ID | ISBN# or Vendor# or EAN or UPC | 
| ACK27 | Agency Qualifier Code | BI = Book Industry Systems Advisory Committee | 
| ACK28 | Source Subqualifier | ACK = BISAC Acknowledgement Code List | 
| ACK29 | Industry Code | AC = Item accepted and shipping (shipping) CO = Cancelled: out of stock (not shipped) ID = Item deleted (not shipped) IB = Item Backordered (not shipped) CA = Cancelled: not yet available (not shipped) OP = Out of print (not shipped) KK = Cancelled: ISBN incorrect/unknown (not shipped) CE = Cancelled: partially filled and shipped; rest cancelled BP = Backordered: partial shipment; balance backordered | 
NTE Freeform Text
| Element | Name | Value | 
| NTE | Segment Identifier | NTE | 
| NTE02 | Freeform Text | Order Correspondence | 
CTT Transaction Totals
| Element | Name | Value | 
| CTT | Segment Identifier | CTT | 
| CTT01 | Number of line items | Number of PO1 segments | 
| CTT02 | Number of Units | Total quantity ordered (sum of PO102) | 
SE Transaction Set Trailer
| Element | Name | Value | 
| SE | Segment Identifier | SE | 
| SE01 | Number of Segments | Number of records in transaction | 
| SE02 | Transaction Set Control Number | Assigned by Sender (unique), (same as ST02) |