Property and equipment is recorded at cost when acquired.  Depreciation is provided principally on the straight-line method over the estimated useful lives of the related assets, which is 3-7 years for equipment, furniture and fixtures, hardware and software and leasehold improvements.   During the nine months ended September 30, 2016, the Company invested $6,140 in shop machinery and equipment, $4,981 in computers and electronics and $2,978 in office furniture and fixtures. Depreciation expense was $25,132 and $10,809 for the nine months ended September 30, 2016 and 2015, respectively. Property and equipment consisted of the following at September 30, 2016 and December 31, 2015: