Table:
|  | 2019 | 2018 |
| --- | --- | --- |
|  | (in thousands) |  |
| Land | $16,561 | $16,561 |
| Buildings | 107,282 | 105,935 |
| Machinery, equipment and software | 834,970 | 752,722 |
| Furniture and fixtures | 29,157 | 27,432 |
| Leasehold improvements | 59,378 | 52,536 |
| Construction in progress | 2,537 | 6,276 |
|  | 1,049,885 | 961,462 |
| Less: accumulated depreciation | 729,669 | 681,641 |
|  | $320,216 | $279,821 |
Paragraphs:
G. PROPERTY, PLANT AND EQUIPMENT
Property, plant and equipment, net consisted of the following at December 31, 2019 and 2018:
Depreciation of property, plant and equipment for the years ended December 31, 2019, 2018, and 2017 was $70.8 million, $67.4 million, and $66.1 million, respectively. As of December 31, 2019 and 2018, the gross book value included in machinery and equipment for internally manufactured test systems being leased by customers was $5.4 million and $5.5 million, respectively. As of December 31, 2019 and 2018, the accumulated depreciation on these test systems was $5.1 million and $5.2 million, respectively.
Question:
What was the accumulated depreciation on the test systems in 2019?
Answer: $5.1 million