Table:
|  | Year Ended |  |
| --- | --- | --- |
|  | April 26, 2019 | April 27, 2018 |
| Balance at beginning of period | $ 40 | $ 50 |
| Expense accrued during the period | 22 | 16 |
| Warranty costs incurred | (22) | (26) |
| Balance at end of period | $ 40 | $ 40 |
| Total warranty liabilities | $ 40 | $  40 |
Paragraphs:
Product warranty liabilities:
Equipment and software systems sales include a standard product warranty. The following tables summarize the activity related to product warranty liabilities and their balances as reported in our consolidated balance sheets (in millions):
Question:
What was the percentage change in the Warranty costs incurred between 2018 and 2019?
Answer: (-22-(-26))/-26 = -15.38