Pivot Table Calculated Fields and Items

Help me add custom calculations to my pivot table:

**Calculation Type Needed:**
- [ ] Calculated Field (creates new measure from existing fields)
- [ ] Calculated Item (creates new item within a field)
- [ ] Show Values As (% of total, difference, running total, etc.)
- [ ] Custom grouping

**Current Pivot Table Structure:**
- Row fields: [list fields in rows]
- Column fields: [list fields in columns]
- Value fields: [list fields in values area]
- Filter fields: [list any filters]

**Calculation Needed:**
[Describe the calculation in plain language]

**Example:**
- Existing fields: [e.g., Revenue, Units Sold]
- New calculation: [e.g., Average Price = Revenue / Units Sold]
- Expected behavior: [how should it work with grouping]

**Specific Scenarios:**
- [ ] Percentage of parent total
- [ ] Year-over-year change
- [ ] Profit margin calculation
- [ ] Weighted average
- [ ] Custom ranking

Please provide:
1. Step-by-step creation instructions
2. Formula syntax for calculated fields
3. Limitations to be aware of
4. Alternative approaches if needed
5. Formatting recommendations
6. Common pitfalls and solutions