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+Purchase Module
+###############
+
+The purchase module define the Purchase model.
+
+
+Purchase
+********
+
+The purchase is mainly defined by a party from which the products will
+be purchased and a list of purchase lines each one containing a
+product and a quantity. Here is a extensive list of the fields, most
+of them are optional or completed with sensible default values:
+
+- Party: The supplier.
+- Invoice Address: The invoice address of the supplier.
+- Supplier Reference: Allow to keep track of the supplier reference
+  for this order.
+- Description: An optional description for the order.
+- Reference: The internal reference of the purchase (will be generated
+  automatically on confirmation).
+- Purchase Date: The date the purchase is made.
+- Payment Term: Define which payment term will be use for the future
+  invoice.
+- Warehouse: Define the warehouse where the shipment will be made.
+- Currency: define the currency to use for this purchase. All product
+  prices will be computed accordingly.
+- Purchase Lines:
+
+  - Type: The type of the line. The default value is *Line* which
+    means that the current purchase contains the fields defined
+    hereunder. The other values of Type (*Comment*, *Subtotal*,
+    *Title*) are used to add extra lines that will appear on the
+    report, thus allowing to easily customise it.
+  - Sequence: Allow to order lines. The value of this field is also
+    updated with a drag and drop between the lines
+  - Product: An optional reference to the product to purchase.
+  - Description: The description of the product to purchase.
+  - Quantity: The quantity to purchase.
+  - Unit: The unit of measure in which is expressed the quantity.
+  - Unit Price: The unit price of the product expressed in the
+    currency of the purchase.
+  - Amount: The amount of the current line (Unit Price multiplied by
+    Quantity).
+  - Taxes: The list of taxes that will be applied to the current line.
+
+- Invoice State: The state of the invoice related to the purchase.
+- Shipment State: The state of the shipment related to the purchase.
+- Untaxed: The untaxed amount.
+- Tax: The tax amount.
+- Total: The total amount.
+- State: The state of the purchase. May take one of the following
+  values: Draft, Quotation, Confirmed, Cancelled.
+- Company: The company which issue the purchase order.
+- Invoice Method: May take one of the following values:
+
+  - Base on order: The invoice is created when the purchase order is confirmed.
+  - Base on shipment: The invoice is created when the shipment is
+    received and will contains the received quantities. If there are
+    several shipments for the same purchase, several invoices will be
+    created.
+  - Manual: Tryton does create any invoice automatically.
+
+- Comments: A text fields to add custom comments.
+- Invoices: The list of related invoices.
+- Moves: The list of related stock moves.
+- Shipments: The list of related shipments.
+
+The *Purchase* report allow to print the purchase orders or to send
+them by mail.