Humans love to measure things, for example temperature, time, distance and calorie intake. Increasingly, we have discovered new ways to apply these measurements to our own bodies. New technologies have allowed us to collect this data more precisely than before and also, perhaps more importantly, to have these measurements available at all times. “Worrying” about our body has become second nature to us so much that we may not even realize how much of our time revolves around tracking ourselves. Every January, magazines, websites, and social media outdo each other in giving weight-loss advice and fueling a guilty conscience. So we are forced to consider working on our “beach body” for the summer. Starting a diet, working out, getting in shape have become body rituals that are usually monitored by bathroom scales. What was it like before private scales stood in every bathroom, which was not that long ago, and how did these instruments become such a crucial element of today’s obsession with weight-loss? Inspired by works from authors such as Michel Foucault, I conducted research on the history of personal self-measurement which is inextricably linked to the development of scales for individual use. What I discovered was that the history of the bathroom scale is also a history of changing moral and social pressures to monitor yourself. Scales are used to discipline the body and reinforce ideas of normality and morality in daily life.

What is today considered a healthy and ideal weight (including the right amount of nutrition and exercise) has been hotly debated for the last 150 years. In the mid-19^th century, statisticians, physicians, health and life insurance companies and health policy dominated this discourse in Germany, which is the case study I focused on in my book. A consensus emerged among this unlikely group of different experts that described slim people as healthier, fitter, more ambitious or more powerful than “overweight” people – a category that was invented in the course of these debates and measuring practices and eventually formed the basis for influential stereotypes that defined who was included in or excluded of society. These discourses of health and morals framed individual choices and options and were often manifested as advice on how to lead a healthy lifestyle, for example through caloric restriction. According to these trends, inventors and engineers developed standardized scales that followed ideas popular in science, economy and politics.

The development of scales began with anthropometric-anthropological measurements in the middle of the 19^th century. As part of examinations performed by the military in Europe, especially in connection with compulsory military service, scientists used simple balance scales to weigh recruits. One soldier would stand on one side, then standard weights were put on the other side until both pans were balanced. Army doctors and social statisticians then determined the average weight of all soldiers, and recommended this figure as a criterion for selection in order to streamline the recruitment process. At around the same time, the Belgian social statistician Adolphe Quetelet (1796–1874) developed a mathematical formula for dividing bodies into categories of “fit” and “unfit” by measuring height and weight. It was rediscovered in the 1970s and is now better known as the Body-Mass-Index (BMI). This formula uses weight in kilograms divided by height in meters squared (kg/m²), however, it was initially not intended to make assertions about health but to optimize the amount of supplies needed by the military to ensure that soldiers stayed in proper fighting form.

Concepts of a “normal” body size became relevant around 1900 outside of the military, for example in school examinations and checkups by panel doctors or medical officers (and around the late mid-19^th century in insurance policies). Anthropometrists and medical scientists aimed to measure the human body in size and shape in order to improve its ability to work and its performance potential. The measurements needed to be as precise as possible in order to enhance health and the life expectancy of entire nations. However, at around the same time, some doctors began to (re)discover “obesity” as a new (and profitable) problem for wealthy citizens. These were willing to pay for treatments at diet clinics, but scales were not yet an everyday item in the public and private spheres. Simultaneously, in Germany, large vending machines appeared at trade exhibitions and on marketplaces. Next to dispensing goods like chocolate, they were also used for weighing. People could insert a coin and weigh themselves – maybe while eating the chocolate. This possibility made the vending machines interesting and promoted their use. Back then, these machines allowed a simple measurement and observation of body weight. They were not yet designed for weight-loss and diet plans, but introduced weighing to a larger public.

In Germany, only in the mid-20^th century did self-measurement become more important as a moral issue and an everyday topic. Until the 1970s, red scales at train stations and public places reminded people to weigh themselves regularly with the inscription “Check Your Weight” [“Prüfe Dein Gewicht!”]. By inserting a coin, the comparison between yourself and the others out there began – symbolized by the average weight. A “normal weight”-chart on the scales quickly showed whether the measured weight was “normal” and healthy, or not. As small scales became cheap through mass production in the 1960s and 1970s, the large-sized scales disappeared from the city’s public spaces. This turned weighing into something private, done quietly and secretly in one’s own bathroom.

Ever since bathroom scales were largely established, we have reflected our body weight by ourselves. Physicians, health policy, handbooks and magazines have long made sure that we know which weight is right for us. Hundreds of inventors have translated these concepts of health and beauty respectively into new inventions and fueled private weighing. They have proposed scales that measure weight as precisely as possible, warn of excessive “under”- and “overweight” with red lamps and even can be integrated into the toilet seat. Bathroom scales were not only intended for the bathroom at home, but in the 1960s also as flexible and light measuring instruments that could be taken on trips and on vacation. In 1968, an inflatable scale was recommended for athletes and actors to stay fit and beautiful. Since the 1960s, microprocessors save the measured weight and provided people with the result from their last weighing to simplify weight-loss tracking. Newer scales act as a body composition monitor and measure the percentages of fat, water, bones and muscles. They interact with apps on the smartphones or smartwatches and indicate your BMI and metabolic age. Hardly any of these apps makes a statement without taking the body weight into account.

Several other factors turned weighing into not only an integral part of everyday life, but a regime. From a technical point of view, there is currently no alternative to bathroom scales, which work precisely and reliably. Beyond that, body weight is considered a first criterion in a medical examination. Social fantasies about a healthy and beautiful body are tied to narratives of happy people and their successful before-and-after stories. These people are not only thin, but also well-toned, tanned and are admired on Instagram (#strongisthenewskinny, #transformation). Their stories seem to record the individual and social success of diets. If the path to the new self is particularly hard and the transformation is documented, the individual wins the struggle for social recognition. In this way, the quantifiable self and optimization are staged in a way that is effective for the public. This is why, today, stepping on bathroom scales, giving thoughts about the index of the scale and slimming is much more than an individual experience. Millions of diets and liposuction in the last years reflect the conditions we live in and stand for a collective fear of fat. There’s nothing else for it but to use scales every day and show off the loss of kilos if people want to fit in society.

When we struggle with indoor cycling bikes again in January, count calories, sign a gym contract (and feel guilty because we show up only once a month), and are happy when the performance log of our health and fitness apps increases – then it means that we voluntarily insert ourselves into a regime that we should examine now and then. In fact, the so-called “right” body weight with its regime is not only inescapable in individual and social terms, but it is a social construction. The fact is that body weight monitoring became an integral part of technical innovations that determine body weight. Over the last 150 years, experts of health like physicians showed several health risks associated with overweight and “obesity”, but new findings on a healthy body weight question previous beliefs. Thus, it is discussed that the 65+ age group should prefer to be moderately overweight rather than having a “normal” BMI. However, the dominant discourse on (preventative) healthcare that we have no option but to bow to this self-surveillance regime if we want to be diagnosed healthy and fit.

What we do make of all of this today? My impression from my research is that the genealogy of scales consists of three episodes that made weighing what it is today. Initially, weighing was a part of scientific studies in which the body and its performance were observed for the purposes of specific institutions such as the military and industry. Second, weighing became a personal affair, a way to compare oneself to others. These processes of the social construction of weighing can be seen as a consequence of modernization, or normalization, medicalization, aestheticization and individualization. A third episode can be described as the integration of scales into our bathrooms and on our smartphones as a permanent fixture of our daily lives. The transformation of these processes into constant companions has helped to implement a regime of (self‑)discipline that dares us to optimize our bodies.