When I now go to the grocery and the butcher weighs out something on the electronic scale, it gives the weight in a system that is only partially English. Rather than using grams and kilograms, it still reads in pounds. But rather than subdivide the pounds into sixteeenths (ounces), it uses base ten increments. Whereas the old balance or spring scale would read "Two pounds, five and three-eights ounces", the electronic one reads "2.336 pound" English fractions are primarily in base two, but then 5280 ft/mile, 3ft/yd, 1760/yd/mile, 4qt/gal, 2pints/qt, 2c/pt, 8floz/c, 2tbsp/floz, 3tsp/tbsp, .etc. just has no consistent basis for division of increments. We've mostly dropped those like 8drams/oz, 60 grains/oz, 6ft/fathom, 3mi/league, 14days/fortnight, etc.
In the Metric system, not only are all measurements calibrated in base ten, all types of measurements are interrelated. For example, one cubic centimeter is virtually the same as a milliliter. A liter of H20 weighs one kilogram and a cc or ml weighs 1 gram. A calorie is the amount of heat needed to raise the temp. of 1 cc or 1 ml by 1 degree Celsius, so to warm 1 liter of liquid H20 from its freezing point (0C) to its boiling point (100C) requires 1000 x 100 calories=100,000 calories. A Newton of force accelerates 1 kg at 1m/sec. For chemistry and physics calculations, the conversion to Kelvin requires only the addition of 273.15 degrees, which is the differential between absolute zero and the freeze/thaw point of H20.
As Bird observed, once you know the system, it's much easier than the English system. Instead of all these arcane conversions, one usually does a small amount of multiplication or division, then moves a decimal several places. Students usually catch on pretty easily. As long as one stays within the metric system, it's not bad. The challenge for many is the conversion back and forth between English and Metric. This is the part that drives students crazy and is the reason the US has never fully embraced the Metric system. One generation would have to make the transition cold turkey, then our posterity would have it easier. The rest of the world has done it (even the English have abandoned the English system). Only we have not. Congress is not willing, because voters are not willing.
A week and a half ago, a new satellite successfully entered orbit around Mars. A couple of years before the rovers landed, we had a $600 million spacecraft that was supposed to enter Mars orbit. There were numerous teams working on the project who all had to send data back and forth about the project. About half did their calculations in English and the others in Metric. Of the teams working together on the complex calculus of final approach to the MOI (Mars Orbit Insertion) burn, one team forgot to convert their data from English to Metric (or vice versa). Because of this oversight, almost a billion dollars slipped right past Mars, headed for the emptiness of space.
