Annual report pursuant to Section 13 and 15(d)

Product warranty - Schedule of Product Warranty Reserve (Details)

v3.20.4
Product warranty - Schedule of Product Warranty Reserve (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Guarantees [Abstract]    
Product warranty period 1 year  
Schedule of Product Warranty Reserve [Roll Forward]    
Warranty reserve, beginning balance $ 205,300 $ 140,600
Warranty provision for units sold 185,696 535,700
Costs of warranty incurred (226,196) (471,000)
Warranty reserve, ending balance $ 164,800 $ 205,300