I believe it’s the max % change from the mean price over a set...

I believe it’s the max % change from the mean price over a set period of time. but, you set the timeframe - which means you set the mean. You would have seen it when brokers issue term sheets and they say comes deal comes with 1:2 options etc and then they value the options using black scholes which seems to conveniently overvalue the actual value - because they set the timeframe for volatility You can do a data dump of current options and list by expiry date, and compare any new options to existing ones with a similar expiry period, similar % difference in current price and exercise price, and come up with a fairy accurate value of option (within 10 - 20% once price has settled down after a week or so from listing) as a percentage of current share price. My spreadsheet had these ALBO at 4c when they were trading about 18c looking at my old notes. 6c sounds fair now.