The spread of metrication around the world in the last two centuries has been met with both support and opposition.
Metrication
The United States of America officially accepted the Metric System in 1878 but United States customary units remain ubiquitous outside the science and technology sector. The metric system has been largely adopted in Canada and Ireland, and partially adopted in the United Kingdom and Hong Kong, without having fully displaced imperial units from all areas of life. In other Anglophone countries such as Australia, Singapore and New Zealand, imperial units have been formally deprecated and are no longer officially sanctioned for use.
Technical arguments
Natural evolution and human scale One argument used by opponents of the metric system is that traditional systems of measurement were developed organically from actual use. Early measures were human in scale, intuitive, and imprecise, as illustrated by still-current expressions such as a stone's throw, within earshot, a cartload or a handful. These measurements' developers, living and working in an era before modern science, gave fundamental priority to ease of learning and use; moreover, the variation permissible within these measurements allowed them to be relational and commensurable: a request for a judgment of measure allowed for a variety of answers, depending on context. In parts of Malaysia, villagers asked the distance to the next village were likely to respond with three rice cookings; an approximation of the time it would take to travel there on foot. Everyone is assumed to know both how long it takes to cook rice, and how fast a person walks. Nominally standard units were also subject to contextual variations. The aune, a French ell used for measuring cloth, depended on the sort of cloth being measured, taking price and scarcity into account: an aune of silk was shorter than an aune of linen. Nowadays most non-metric units are standardised to fixed values, which eliminates the disadvantage of imprecision while retaining the advantage of human scale. For example, the advocacy group British Weights and Measures Association has argued that metrication led to greater complexity for consumers accustomed to imperial units because, unlike the ounce, a single gram is too small a measurement in everyday life.
Divisibility Metric opponents cite easier division of customary units as one reason not to adopt a decimalised system. For example, those customary units with ratios of 12 and 16 have more proper factors, {2, 3, 4, 6} and {2, 4, 8}, than the metric 10: {2, 5}. However, easily divisible numbers can be selected for use with metric units, e.g. 300 mm and its multiples. The number of times that these odd fractional numbers would come up has also been pointed out as a counterargument; in construction and engineering, for example, measurements would not only be likely to be in integers to begin with, but would also rarely be needed to convert to another unit. The main disadvantage cited by critics of customary measures is the proliferation of units, their (sometimes) non-unique definition and the difficulty in remembering the ratios between them.
Duplication in naming and usage A common argument for the metric system is that it avoids duplication of naming and the associated confusion. The most commonly cited example is pound (force) vs pound (mass), which have the same symbol and are both commonly written simply as "pounds", which can lead to costly and dangerous shipping and engineering errors. Opponents of metrication argue that this issue only occurs due to misuse; when used "properly", there is no cause for confusion. Separately, it is also argued that customary units feature too many overlapping units. The most commonly cited examples are in liquid volume, where metric has simply litres while customary has gallons, pints, quarts, fluid ounces, and the rarely used gill, and minim, all of which cover volumes of liquid in similar ranges. Metrication opponents argue that this allows for easily listing amounts that are awkward in metric (e.g. 1 liquid pint = 568.3 mL in the UK and 473 mL in the US) but are commonly used and avoids "excessive" use of decimals and fractions. These problems however would disappear if metrication continues and they cease to become as common, replaced with a metric equivalent. For example, a pint is often rounded down to 0.5 L, otherwise sometimes rounded up to 0.6 L.
Industry-specific product sizing Metric-opposed artisans and practitioners may be concerned by certain dimensions being less memorable with metric units. As the table below shows, industries have addressed such concerns by using a "hard conversion" into metric units of the dimensions involved. (Metric conversion also gives the opportunity to "rationalize" the range of sizes which are available.):
Political arguments
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