Wikipedia:Reference desk/Archives/Mathematics/2019 October 29

= October 29 =

Nautical Metric
Was there a change from Nautical miles and knots etc to a more standardised metric type system? Thanks — Preceding unsigned comment added by 81.131.40.58 (talk) 08:34, 29 October 2019 (UTC)
 * According to what I could find on-line, apparently not. A nautical mile is defined (more or less) as a one minute arc one a great circle route, and since nautical charts still use degrees and minutes it's easier to correlate the charts with distance if you use Nautical miles your unit of distance. I suppose if nautical charts where converted to use grads instead of degrees then converting to kilometers might be more feasible. However, since distances are being calculated by computers nowadays I guess whether nautical miles are easier or not is increasingly irrelevant. --RDBury (talk) 21:30, 29 October 2019 (UTC)
 * These days (since 1929, in fact) a nautical mile is a metric unit, sort of, in that it's defined simply as 1852 meters, although it is not part of the SI.  This length is equal to 40,000/21,600 km (thus corresponding to 1 minute of arc along a circle whose circumference is 40,000 km) rounded to the nearest whole meter. --76.69.116.4 (talk) 01:47, 30 October 2019 (UTC)
 * Well, few people would say inch is a metric unit, even though it is defined as being equal to 25.4mm. A more standardised metric type system can have three meanings:
 * that it follows the metric system or SI
 * that it has a precise metrologic definition (though not necessarily based on SI, see for instance the FPS system)
 * that it uses decimal units (again, not necessarily based on SI - for instance the gradian is not SI-based)
 * The nautical mile is not part of SI, but it has a precise definition (based on the SI meter). As to the decimality, it is hard to say, because it is not often used with subdivisions. My guess is that it used for distances at sea, not for distances between stars or bacteria, so all useful values will be somewhere between 0.1 and 1000, making subdivisions not so useful. I would say it is, as the cable length and the fathom are decimal subdivisions (1/10 and 1/1000) of the nautical mile.  Tigraan Click here to contact me 10:28, 30 October 2019 (UTC)
 * Indeed; it is correlated to the actual metric system, but it is not part of the metric system. For most units, the sine qua non for being a metric unit is that it is based on the decimal system; that is when related to smaller and larger units for the same measurement, it can be done so purely as a multiple of ten.  Nautical miles are not related to other measurements of length by multiples of ten; and there are no "millinauticalmiles" or "kilonauticalmiles".  -- Jayron 32 12:28, 30 October 2019 (UTC)

Relative timing of withdrawal and interest accrual in a payout annuity
In a payout annuity, does the interest accrue before or after the disbursal?--Wikimedes (talk) 17:13, 29 October 2019 (UTC)
 * It depends entirely on the contract that defines it. This may vary from institution to institution.  In other words, read the fine print on your specific financial instrument.
 * And, like everything else, this may have tax implications, especially if your annuity involves non-trivial sums.
 * Nimur (talk) 14:55, 30 October 2019 (UTC)
 * True enough. Annuity implies that interest accrues before disbursal, so I'll work with that for hypothetical situations.--Wikimedes (talk) 23:45, 30 October 2019 (UTC)