pre_text: 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):
table: Year Ended
table: April 26, 2019 April 27, 2018
table: Balance at beginning of period $ 40 $ 50
table: Expense accrued during the period 22 16
table: Warranty costs incurred (22) (26)
table: Balance at end of period $ 40 $ 40
table: Total warranty liabilities $ 40 $  40
question: Analyse this data from a financial earnings document. What was the change in expense accrued during the period between 2018 and 2019?