[Pisces]

Some metric vs imperial transformation rules:

1 foot = 0.3048 meter ; 1 meter = 3.28 foot

Or as quick rough conversion for governmentwork:

in foot: meters times 3 + a tenth of it (10%)

120m: 120x3 + 36= 396 feet ( or if exact: 120m/0.3048m= 393.7 feet)

in meters: feet - a tenth of it (10%), dividing then by 3
270 feet: 270 feet - 27= 243, divide by 3 is 81 meters.

1 yard = 3 foot, so you just have to take care of that 10th or 10% in the calculation. A yard is just 8-9% short of a meter.

1 yard = 3 x 0.3048m = 0.9144m

1m = 1.09 yards which is close to 1.1 yards.

400m in yards: 400m + 40m = 440 yards (versus 437.4 exact yards)

650 yards in meters: 650 yards - 65 yards = 585 m (versus 594.4 meters exact)

This last isn't very exact. But you don't need to have that precision usually. Just be close enough to get the biggest broadside angle of the target to hit into.

Nautical miles:

1 nautical mile = 1852 meters, just short of 2 kilometer.

Or 1 nautical mile is roughly 8% short of 2 kilometer. Or 2 kilometer is about 7.5% longer than 1 nautical mile.

nautical miles to kilometers: times 2, then subtract 8% of that result
50 nm = 2 x50 kilometers, then - 8x2x50/100= 100-8 km = 92 km( versus 92.6 km exact)

kilometers to nautical miles:
nautical miles = add 8% of kilometers, then halve of that.

300 kilometers in nautical miles: 300 + 24= 324, then halve = 162km (versus 161.98 nautical mile exact)

As for speeds: speed in meters per second: 1 m/s = 1.944 knots (=3600/1852); or roughly 2 knots. (close within 3%)

So measure length in meters, divide speed across the (fixed, stationary) line by time in seconds. Times 2 to get knots.