NOTE 7—PROPERTY, PLANT AND EQUIPMENT

Significant components of property, plant and equipment are as follows (in thousands):


September 30,	2018		2017

Land and land improvements	$	13,132	$	16,139
Buildings and improvements		57,959		52,625
Machinery and other equipment		81,727		73,235
Software		84,631		62,297
Leasehold improvements		11,991		13,298
Construction and internal-use software development in progress		12,888		23,156
Accumulated depreciation and amortization		(144,782)		(127,530)
	$	117,546	$	113,220

As a part of our efforts to upgrade our current information systems, early in fiscal 2015 we purchased new enterprise resource planning (ERP) software and began the process of designing and configuring this software and other software applications to manage our operations.

Costs incurred in the development of internal-use software and software applications, including external direct costs of materials and services and applicable compensation costs of employees devoted to specific software development, are capitalized as computer software costs. Costs incurred outside of the application development stage, or that are types of costs that do not meet the capitalization requirements, are expensed as incurred. Amounts capitalized are included in property, plant and equipment and are amortized on a straight-line basis over the estimated useful life of the software, which ranges from three to seven years. No amortization expense is recorded until the software is ready for its intended use.

Through September 30, 2018 we have incurred costs of $135.8 million related to the purchase and development of our ERP system, including $22.5 million, $40.6 million, and $45.2 million of costs incurred during fiscal years 2018, 2017 and 2016, respectively. We have capitalized $7.5 million, $16.7 million, and $20.3 million of qualifying software development costs as internal-use software development in progress during fiscal years 2018, 2017, and 2016, respectively. We have recognized expense for $15.0 million, $23.9 million, and $24.9 million of these costs in fiscal years 2018, 2017, and 2016, respectively, for costs that did not qualify for capitalization. Amounts that were expensed in connection with the development of these systems are classified within selling, general and administrative expenses in the Consolidated Statements of Operations.

Various components of our ERP system became ready for their intended use and were placed into service on April 1, 2016, October 1, 2016, October 1, 2017, and April 1, 2018. As each component became ready for its intended use, the component’s costs were transferred into completed software and we began amortizing these costs over their seven-year estimated useful life. We continue to capitalize costs associated with the development of other ERP components that are not yet ready for their intended use. The final phase of implementation will begin in early fiscal 2019.

Our provisions for depreciation of plant and equipment and amortization of leasehold improvements and software amounted to $19.5 million, $17.8 million and $11.0 million in 2018, 2017 and 2016, respectively. Generally, we use straight-line methods for depreciable real property over estimated useful lives ranging from 15 to 39 years or for leasehold improvements, the term of the underlying lease if shorter than the estimated useful lives. We use accelerated methods (declining balance and sum-of-the-years-digits) for machinery and equipment and software other than our ERP system over estimated useful lives ranging from 5 to 10 years.