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 derivative liabilities because they have registration rights which could require a cash settlement 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 June 30, 2019 and December 31, 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 June 30, 2019 and December 31, 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 three months ended June 30, 2019 and 2018.

Common Stock Warrants

The Company has issued certain warrants to purchase shares of common stock, which are considered derivative liabilities because they have registration rights which could require a cash settlement and are re-measured to fair value at each reporting period in accordance with accounting guidance. At June 30, 2019 and December 31, 2018, approximately $0.9 million of the derivative liability was calculated using the Black-Scholes-Merton valuation model. At June 30, 2019 and December 31, 2018, no significant amount of the derivative liability was calculated using the Monte Carlo Simulation valuation model.

The assumptions used in estimating the common stock warrant liability using the Black-Scholes-Merton valuation model as of June 30, 2019 and December 31, 2018 were as follows:

The assumptions used in estimating the common stock warrant liability using the Monte Carlo Simulation valuation model at June 30, 2019 and December 31, 2018 were as follows:

In addition, if any time after the second anniversary of the issuance of the warrant, both: (1) the 30-day volume weighted average price of the Company’s stock exceeds $3.00; and (2) the average daily trading volume for such 30-day period exceeds $0.4 million, the Company may call this warrant for $0.01 per share. For those warrants that have a call provision, management believes the Monte Carlo Simulation valuation model provides a better estimate of fair value for the warrants issued during 2018 and 2017 than the Black-Scholes-Merton valuation model.

Other Financial Instruments

The Company’s recorded values of cash and cash equivalents, accounts receivable, 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.