Weighing and Measuring
The subject of weights and measures is a slightly complicated one, as there are three different systems in common use - metric weight, imperial weight, and volume. Most cooks in the USA measure in cups, i.e. by volume of ingredient. However, this system is not ideal if we want a consistent, predictable finished product because the amount of flour in a cup varies according to how compacted it is. A quick Google search reveals that one cup of flour can vary from 100 to 150g, depending on who is doing the measuring - clearly allowing a potential variation of 50% is not the best way to go about writing recipes.
A pint is not a pint ...
The imperial system of pounds, ounces, and pints also has disadvantages. If you have a recipe for two loaves of bread using 1lb 12oz of flour, and you decide you want to make three loaves, the calculation for adding 50% is much less straightforward than it would be for 800g flour in the metric system. Also, if you ever use a recipe which includes pints or fluid ounces, you have to be sure which sort of pints or fluid ounces it means. A British fluid ounce is 28.41 ml while a US fluid ounce is 29.57 ml. A British pint is 20 British fluid ounces, while an American pint is 16 American fluid ounces! At least the British fluid ounce is exactly the volume of one ounce of water - the American one is slightly more.
The answer to these problems is to use the metric system of grams/kilograms for weight(mass) and millilitres/litres for volume. The metric system uses base 10 throughout rather than base 16 or base 20, so calculations are much easier. Bakers' percentages are a doddle in metric: if you have 1 kg of flour and you want 60% hydration for a sandwich loaf, you need 600ml of water, which of course weighs 600g so it's easy to measure accurately.
I hope you are convinced of the benefits of using the metric system. If you don't have a kitchen scale that measures in grams, you can buy one quite cheaply from Amazon: Kitchen Scales - UK
The one exception to the "metric is best" rule is when you are measuring small quantities of salt or yeast for a recipe. In this case, it is easier to use a volume measurement than to weigh something that is under 10 grams. All the recipes on this site will use teaspoons/tablespoons. A teaspoon is roughly equal to 5 millilitres (in fact, not surprisingly, there is a slight difference between the UK imperial teaspoon and the US teaspoon but the difference is small enough to ignore in home baking quantities) and a tablespoon is roughly 15 ml. Again, you can buy a good set of measuring spoons through Amazon: Measuring Spoons - UK