Annual report pursuant to Section 13 and 15(d)

Accrued Expenses - Changes in Accrued Warranty Obligations (Details)

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Accrued Expenses - Changes in Accrued Warranty Obligations (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Accrued Expenses      
Accrued Warranty Obligations, beginning of period $ 98,893 $ 218,047 $ 167,503
Reductions for Settling Warranties (193,503) (204,583) (257,173)
Warranties Issued During Period 238,508 85,429 307,717
Accrued Warranty Obligations, end of period $ 143,898 $ 98,893 $ 218,047