Table:
|  | PSG | ASG | ISG | Total |
| --- | --- | --- | --- | --- |
| For year ended December 31, 2019: |  |  |  |  |
| Revenue from external customers | $2,788.3 | $1,972.3 | $757.3 | $5,517.9 |
| Segment gross profit | 976.0 | 794.8 | 275.4 | 2,046.2 |
| For year ended December 31, 2018: |  |  |  |  |
| Revenue from external customers | $3,038.2 | $2,071.2 | $768.9 | $5,878.3 |
| Segment gross profit | 1,110.1 | 878.3 | 317.1 | 2,305.5 |
| For year ended December 31, 2017: |  |  |  |  |
| Revenue from external customers | $2,819.3 | $1,950.9 | $772.9 | $5,543.1 |
| Segment gross profit | 959.8 | 817.8 | 302.6 | 2,080.2 |
Paragraphs:
Note 3: Revenue and Segment Information
Revenue recognized for sales agreements amounted to $5,492.0 million and $5,849.0 million for the years ended December 31, 2019 and 2018, respectively. Revenue recognized for product development agreements amounted to $25.9 million and $29.3 million for the years ended December 31, 2019 and 2018, respectively.
The Company is organized into three operating and reportable segments consisting of PSG, ASG and ISG. The Company's wafer manufacturing facilities fabricate ICs for all business units, as necessary, and their operating costs are reflected in the segments' cost of revenue on the basis of product costs. Because operating segments are generally defined by the products they design and sell, they do not make sales to each other.
The Company does not allocate income taxes or interest expense to its operating segments as the operating segments are principally evaluated on gross profit. Additionally, restructuring, asset impairments and other charges, net and certain other manufacturing and operating expenses, which include corporate research and development costs, unallocated inventory reserves and miscellaneous nonrecurring expenses, are not allocated to any segment.
In addition to the operating and reportable segments, the Company also operates global operations, sales and marketing, information systems and finance and administration groups. A portion of the expenses of these groups are allocated to the segments based on specific and general criteria and are included in the segment results.
Revenue and gross profit for the Company’s operating and reportable segments are as follows (in millions):
Question:
What is the change in PSG Revenue from external customers from year ended December 31, 2018 to 2019?
Answer: 2788.3-3038.2 = -249.9