One of the things I learned in the Navy that I use on a fairly regular basis is the ability to calculate sines in my head.  I dunno why they don't teach this in school, but it comes in damned handy.


For angles up to 40 degrees, sinX = X/60


For angles more then 40, sinX = (X+25)/100




So sin22=22/60 that's a tad bit over 1/3 or if I do the long division, I get .38.  




and sin 60, that's 60+25 = 85%.  And at 75 degrees, the sin is 1


 

Dude, it's Thursday and I've been drinking ... I can't handle this

And what do u use this for?

 
It comes in handy for showing off.  But I use it a lot to cross-check things at work or even at the hardware store.






What's the corrected range for a shot fired at a 15 degree angle?  That's range times cos of 15.  Which is range times sin (90-angle=75deg) = 1 x range.   Answer:  no correction necessary.



 


How much deeper is the low pressure blower at the back of a 500' long sub if the ship is at a 2deg angle?  2/60=4%, so ~20ft.  33ft is 15psi, so the back pressure is about 10psi higher.


 

Good info.

Today's generation isn't taught to multiply 2*2 in their head, so this is way outside the norm for them unfortunately.

Nice trick!

One I use a lot is for figuring area of circles- D^2 x .7854.  Cause circles are basically just squares with the corners knocked off.

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I guess this is just for approximation?

20 sin is .34202014 but your formula gives .3333_

It's a neat trick, don't get me wrong.  But, not accurate enough for the stuff I do.

Still. I like anything math.