10.           Balance Sheet Detail:

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Equipment and leasehold improvements consist of the following:

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During the three months ended March 31, 2021 and 2020, the Company recorded depreciation and amortization expense of $0.3 million and $0.2 million, respectively.

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In limited circumstances, the Company offers extended payment terms to customers for periods of 12 to 36 months. The related customer receivables are classified as accounts receivable long-term and discounted to their present value at prevailing market rates at the time of sale. In subsequent periods, the accounts receivable is increased to the amounts due and payable by the customers through the accretion of interest income on the unpaid accounts receivable due in future years. The amounts under these long-term accounts receivable due within one year are reclassified to the current portion of accounts receivable. At times the Company sells receivables to a financial institution on a non-recourse basis for cash, less a discount. The net proceeds from such sales are included in the operating section of the statement of cash flows as changes in accounts receivable. Accounts receivable long term, net consists of the following:

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The undiscounted cash flows to be received by the Company relating to these accounts receivable long-term expects to be $1.5 million, $0.1 million and $0.1 million during the 12-month periods ending March 31, 2022, 2023 and 2024, respectively.

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Accounts payable and accrued expenses consist of the following:

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