Additional Information
Only in the Imperial system of measures are mixed units "allowed".
That is, measurements like
5 hundredweight 2 quarters 16 pounds
2 tons 15 hundredweight 3 stone
etc.
Note that the singular and plural forms of "hundredweight" are the same;
this also holds true for the abbreviation "cwt" and for "stone".
In the SI or metric system, mixed measures are "not allowed", and they are certainly not necessary. Something like
15 metres 78 centimetres 3 millimetres
is expressed as
15.783 metres
However, in spite of the valid arguments for use of the metric system,
there also exist valid arguments for continued use of portions of the Imperial system in certain contexts.
One of those contexts is the ancient English tradition of changeringing,
using large bells hung in a particular manner in church towers.
(Though there are some other types of towers which hold such bells, and a different style of ringing changes
can be done on handbells, it is the tower bells which are relevant to the present point.)
Thousands of towers, and tens of thousands of bells and ringers, are involved in The Exercise,
not only in England but also in the rest of the British Isles and in North America, Australia, New Zealand and South Africa.
Hundreds of years of records regarding not only these bells but also various performances upon them
are based upon a customary subset of the British Imperial system of weights.


The Imperial weight definitions are as follows:
16 ounces = 1 pound [lb]
14 pounds = 1 stone
28 pounds = 2 stone = 1 quarter [qtr]
112 pounds = 4 quarters = 1 hundredweight [cwt]
2240 pounds = 20 hundredweight = 1 ton
In changeringing parlance, ounces and stones are not used at all; hence their absence from this calculator.
Also, tons are used only for approximate weights of huge bells; cwt is the basic unit for exact weights,
as well as for approximate weights of ordinary bells.
Now consider the measurement of
6777 pounds
That could be stated by a ringer (or in ringing records) as
3 tons
OR
61 cwt
OR
60 1/2 cwt
OR
6021
The first figure is an approximation to the nearest ton, the second figure is an approximation
to the nearest hundredweight, and the the fourth figure is an exact statement.
Note that in the last case the units are not stated and the three values are separated by hyphens.
By convention, all exact weights of 1 cwt or more are written thus,
even if the second and/or third values are zero.
(In tables of information, spaces may be used instead of hyphens.)
This convention has the disadvantage that in some contexts it is unclear whether a weight is exact or approximate.
3500 is probably approximate, but 2220 could be either exact or approximate.
