Note 2 - Summary of Significant Accounting Policies - Stock Options, Valuation Assumptions (Details)	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020
Non Plan [Member]
Risk free interest rate	1.73%	0.88%
Expected volatility	124.00%	131.00%
Expected dividend yield	0.00%	0.00%
Life in years (Year)	10 years	10 years
2018 Equity Incentive Plan [Member]
Expected dividend yield	0.00%	0.00%
Life in years (Year)	10 years	10 years
2018 Equity Incentive Plan [Member] \| Minimum [Member]
Risk free interest rate	0.93%	0.88%
Expected volatility	123.00%	131.00%
2018 Equity Incentive Plan [Member] \| Maximum [Member]
Risk free interest rate	1.73%	1.90%
Expected volatility	124.00%	133.00%

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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- Definition

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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- Definition

The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
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-URI http://asc.fasb.org/extlink&oid=122041274&loc=d3e301413-122809

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