# 'Calculation' Items {% hint style="info" %} Use the 'sub total' element to add the balances of a series of preceding line items and apply a calculation item. The sub total item is added from the Item selector. {% endhint %} ### Charge Item This Item can be used to add an arbitrary charge as a percentage of the preceding line Item i.e. a sub-total. It can also represent a fixed charge. The Charge Item can be used to bill for the supply of goods or services by a third party. Use the Purchasing tab to set the costs and supply details. #### Accounting The Charge item can post to an Income and an Expense Account. ### Discount Item This Item is used to apply a discount to the preceding line Item i.e. a sub-total. See ‘[Discounts](/sales/sales-orders/discounts.md)’. #### Accounting The Discount Item can post to an Income or an Expense Account. ### Mark up Item The Markup Item is used to apply a markup to the preceding line Item of a fixed amount or a percentage. #### Accounting The Mark up Item posts to an Income account. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://helpwith.salesorder.com/products-services/items-which-ones/calculation-items.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.