What was the change in Product and service revenue recognized at point in time between 2018 and 2019?
{"Product and service revenue recognized at point in time": {"2019": 786918, "2018": 715055, "2017": 667440}, "Extended warranty and service contracts recognized over time": {"2019": 2030, "2018": 3837, "2017": 3572}, "Total": {"2019": 788948, "2018": 718892, "2017": 671012}}
product_and_service_revenue_recognized_at_point_in_time_2019 = df["Product and service revenue recognized at point in time"]["2019"]
product_and_service_revenue_recognized_at_point_in_time_2018 = df["Product and service revenue recognized at point in time"]["2018"]
answer = product_and_service_revenue_recognized_at_point_in_time_2019 - product_and_service_revenue_recognized_at_point_in_time_2018