Short cut to approximating IV,HV

Some of the benefits of sharing market information is the trainer achieves more clarity on specific concepts.

1. In delivering NSE program on derivatives , I came across a shortcut to approximating Implied Volatility(IV) and Historical Volatility(HV).
2. Normal approach to caluculating HV involves statistical caluculation.
3. Devangshu Datta of BS describes a thumb rule approach to estimating HV. It involves calculating the daily  HIGH - LOW range as a % of Futures settle price. You can take say, a 20-day moving average of this in order to get a smoother value. This can be used as a proxy for HV.
4. For estimating IV, We can take nearest to money call option and nearest to money put option premiums and calculate the breakevens to derive a range. For ex Nifty at 5280, 5300C (premium 100) and 5250 P (128) can be considered. A strangle breaks even outside 5558 -5022. This 536 points can be expressed as a percentage of NIFTY 5300 approx 10% as a estimate of IV. 
5. Black-Scholes options caluculator gives more precision but a thumbrule approx can be done as above