Salesforce CPQ Quote Line field Additional Discount Unit

1. Navigate to the Quote Line Object.
2. Create a new Picklist Field with the API Name AdditionalDiscountUnit. 
3. Determine what picklist values your users should be allowed to use and add the picklist values to Additional Discount Unit. Supported picklist values: Percent, Amount, Unit Override, Total Override. Note: 'Amount' is required to be an active value in the picklist.
4. Navigate to a Quote and click Edit Lines.
5. Verify that Additional Disc. field’s picklist has the values entered in step 3.

Example:

1. After following the implementation steps ensure that AdditionalDiscountUnit has all 4 picklist values active (Percent, Amount, Unit Override, Total Override)
2. Navigate to a Quote and click Edit Lines.
3. Select the Additional Discount value type from the picklist (Percent, Currency, Unit, Total).
4. When you change the discount method and enter in the override value, the amount will automatically change based on the new method selected. You can then select Calculate, Quick Save, or Save to apply that discount to the Customer Prices accordingly. An example is given below for an item with a list unit price of $25,000 and an initial discount method of 85%.

Considerations:

• Reordering this picklist or removing picklist values from this picklist will change what users see in the line editor. For example, if you removed 'Percent' picklist value, users could no longer apply a Percentage discount and would be limited to applying an Amount, Unit Override, or Total Override discount in the quote line editor.
• If the ‘Amount’ picklist value does not exist for AdditionalDiscountUnit field, when the Account’s Renewal Pricing Method is set to Same or Uplift, Salesforce CPQ will still use the quote line’s Additional Discount Amount field to achieve the Same pricing as what was originally quoted. More info can be found in the Renewal Pricing Method Field Mapping Behavior article.
• When using Quote Line Target Customer Amount (Unit Override or Total Override) it is considered best practice to use 'Unit Override' to avoid rounding errors. While 'Total Override' is meant to help you goal seek to the correct additional discount, the combination of quantity and unit price may cause minor rounding issues. 
• The AdditionalDiscountUnit picklist value will only impact discounts input by users in the Quote Line Editor UI. Values input to Additional Discount fields using any other method (e.g. via QCP, Price Rules, Line Import, etc) will be treated as-is for the data type of the respective fields, Additional Discount (%) or Additional Discount (Amt).
• When setting the Additional Discount Unit field as Unit or Amount Override, the value of the SBQQ__AdditionalDiscountAmount__c will only be available after the calculation. In order to use SBQQ__AdditionalDiscountAmount__c in Price Rules or in a Quote Calculator Plugin (QCP), the field must be referenced on an After Calculation event.
• When using the CPQ special field ApplyAdditionalDiscountLast__c with AdditionalDiscountUnit__c, ensure the Amount picklist value exists. If the Amount picklist value does not exist when both of these special fields have been enabled, additional discounts will not calculate correctly.