pre_text: 17. Financial Information About Segments Our operations are divided into two reportable segments: Products and Licensing and Technology Development. The Products and Licensing segment develops and sells products or licenses technologies based on commercially viable concepts developed by the Technology Development segment. The Products and Licensing segment derives its revenue from product sales, funded product development and technology licenses. Our engineers and scientists collaborate with our network of government, academic and industry experts to identify technologies and ideas with promising market potential. We then compete to win fee-for-service contracts from government agencies and industrial customers who seek innovative solutions to practical problems that require new technology. The Technology Development segment derives its revenue primarily from services. The Technology Development segment provides applied research to customers in our areas of focus. Our President and Chief Executive Officer and his direct reports collectively represent our chief operating decision makers, and they evaluate segment performance based primarily on revenue and operating income or loss. Information about the results of operations for each segment is set forth in the table below. There were no significant inter-segment sales during the years ended December 31, 2019 and 2018. During the years ended December 31, 2019 and 2018, 32% and 24%, respectively, of our total sales took place outside the United States. Customers in China represented 11% of total revenues in the year ended December 31, 2019, while no other single country, outside of the United States, represented more than 10% of total revenues in the year ended December 31, 2018.
table: Years ended December 31,
table: 2019 2018
table: Products and Licensing revenue $44,491,041 $21,949,689
table: Technology Development revenue 26,024,674 20,967,556
table: Total revenue $70,515,715 $42,917,245
table: Products and Licensing operating income $1,807,616 $499,323
table: Technology Development operating income  1,507,405 378,212
table: Total operating income $3,315,021 $877,535
table: Depreciation, Technology Development $397,296 $379,952
table: Depreciation, Products and Licensing  $552,285 $273,185
table: Amortization, Technology Development  $91,185 $130,765
table: Amortization, Products and Licensing $1,462,525 $418,349
question: Analyse this data from a financial earnings document. What is the change in Products and Licensing revenue between December 31, 2018 and 2019?