A lot easier than with a furuno that’s overheated and left me with only a chartplotter for the remainder of the day
www.scmarine.org
www.joinrfa.com
Luke 8:22-25
a quick fin count gets you halfway there, and eye/mouth position eliminates everything but the almaco/greater AJ question. pointy dorsal fin takes care of that.
no need for nautical PCR…
nauti PCR 
Mountain Dew or Crab Juice. Eeww…sheesh…I’ll take a crab juice.