5. Fair Value Measurements

Financial Instruments Measured and Recorded at Fair Value on a Recurring Basis

The Company has issued certain warrants to purchase shares of common stock, which are considered mark-to-market liabilities and are re-measured to fair value at each reporting period in accordance with accounting guidance. Fair value is based on the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date, under a three-tier fair value hierarchy which prioritizes the inputs used in measuring fair value as follows:

The Company classifies assets and liabilities measured at fair value in their entirety based on the lowest level of input that is significant to their fair value measurement. No financial assets were measured on a recurring basis as of December 31, 2019 and 2018. The following tables set forth the financial liabilities measured at fair value on a recurring basis by level within the fair value hierarchy as of December 31, 2019 and 2018.

The Company did not have any transfers of assets and liabilities between Level 1 and Level 2 of the fair value measurement hierarchy during the years ended December 31, 2019 and 2018. The following table presents a reconciliation of the derivative liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) during the years ended December 31, 2019 and 2018 (in thousands):

Common Stock Warrants

As of December 31, 2019, and 2018, approximately $0.2 million and $1.6 million respectively, of the derivative liabilities were calculated using the Black-Scholes-Merton valuation model. As of and December 31, 2019 and 2018, no significant amount of the derivative liability was calculated using the Monte Carlo valuation model.

The assumptions used in estimating the common stock warrant liability using the Black-Scholes-Merton valuation model as of December 31, 2019 and 2018 were as follows:

Other Financial Instruments

The Company’s recorded values of cash and cash equivalents, account and other receivables, accounts payable and accrued liabilities approximate their fair values based on their short-term nature. The recorded value of notes payable approximates the fair value as the interest rate approximates market interest rates.