The practice of locating natural gas and petroleum deposits has been transformed dramatically in the last 20 years with the advent of extremely advanced, ingenious technology. In the early days of the industry, the only way of locating underground petroleum and natural gas deposits was to search for surface evidence of these underground formations.
Thumb Safety. No, the problem with a Thumb Safety is it's a Minor Motor Skill the way your brain see's it. Under a stressful situation you may loose all minor motor skills. All my guns I train with and I train consistantly, do not have any safeties.
Rule of thumb. A rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination. It is based not on theory but on practical experience.