1. From the management settings for the custom object, click Edit.
2. Select the Track Field History checkbox.Tip When you enable tracking for an object,customize your page layouts to include the object’s history related list.
3. Save your changes.
4. Click Set History Tracking in the Custom Fields & Relationships section.This section lets you set a custom object’s history for both standard and custom fields.
5. Choose the fields you want tracked.You can select up to 20 standard and custom fields per object. You can’t track:Formula, roll-up summary, or auto-number fieldsCreated By and Last Modified By
6. Formula, roll-up summary, or auto-number fields
7. Created By and Last Modified By
8. Click Save.Salesforcetracks history from this date and time forward. Changes made prior to this date and timeare not included.