Complete and incomplete covers in engineering

I confess I have been irritated my whole life about car dashboard controls for heating and cooling because they are an incomplete cover for the complexity that is going on inside. It has been a rough few decades for user interface enthusiasts!

What is a complete cover? It is a layer or shell over some machine complexity that completely hides it and does not let any of the complexity out. A cover is incomplete if it forces you to understand what is going on underneath, or if it is confusing when you do not understand, or if the cover is insufficient to operate all aspects of the machine. A cover can be thick or thin – the thicker the cover, the more it changes the paradigm of the machine interaction. A cover is optimal when it is complete, regardless of whether it is thick, thin, or absent. Sometimes it is optimal to have no cover.

I will explain this with some of examples, starting with a mechanical mercury thermostat. There are three kinds of people in relation to these devices: (1) Those with a gut fear reaction when they look at dials and numbers; (2) those who understand the two exposed dials – measured temperature and set point – but do not know or care how it works inside; and (3) those who understand that the rotation of the temperature-sensitive coil which is superimposed on the rotation of the set point tips a mercury switch, that the bi-stable 2-lobed shape of the mercury chamber affects the temperature swing, and why mercury is used in the first place. It is a lovely thing, but not really the scope of this paper. I am mainly concerned with the middle category of people who are functional operators of the cover and what kind of cover it is.

The thermostat is a complete cover because you can operate every aspect of the heater with it, without needing to know how it works. It is also a fairly thick cover in the sense that it translates one paradigm to another. The actual heater requires an on/off switch to work, thus the only language it understands is on/off. But the thermostat exposes a set point to the user. It translates the language of on/off to the language of set points. Someone could replace the whole heater and wiring with a different inside paradigm but leave the exposed paradigm there, and the user would not need to know that anything changed, because the operation stays the same. In many systems – especially software systems, the replaceability of layers is an important design point, and complete coverage is one of the factors that makes it possible.

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On weeds and keystones

Las Vegas is an optical illusion. At first it looks poor; the city eye is drawn to cracks in the pavement and boarded up businesses, and one expects to feel poverty. Once an ornate and grand city, larger than Albuquerque, the town now shows age and depleting resources with fewer people. But then nothing bears out the expected feeling, and over time the eye learns to see different things – the beauty that is still there.

From my one window I see weeds, graffiti, and a muddy puddle in an empty lot. And I also see hand-set bricks in arches with stone sills, keystones, quatrefoils, with elms and aspens. Out the other window there’s a quintessential abandoned factory with sawtooth shaped roof, a highway bridge, and a stone hotel with a belfry and artistic parapet. With so much variation there is choice – what do I choose to see?

It reminds me of Pisa, Italy. I still have a picture I took of a goat eating weeds in a neglected brick-strewn lot, next to a crumbling plaster wall, in bleating distance from the throngs of leaning-tower photographers.

On a dumpster diving errand today I found nothing, and everything was surprisingly clean. Investment in the big city is equated with wealth, safety and the standard of living. But in reality, the distribution of money does not entirely control the use of time. New cities in the west exist because of greed, not because of natural necessity in the way port cities exist. Subdividing land, the innumerable rules, and smooth new concrete all make someone rich and define the city. Homelessness is illegal, and those who can’t meet the wealth standard congregate only where enforcement of all the rules is lacking, where there is less safety. So the city is an engine of separating haves from have-nots to its very core. And it fogs ones brain with the urgency of the struggle to have.

Politics in the west is the art of profiting from subdivision and controlling public utilities. The desert is almost free, but the value of a residential zoned quarter-acre with water and electricity is enormous. We don’t all share in that value. The winners are the ones who approved the subdivision plat on their own land.

On my errand the thing I realized is that if I myself owned things like sidewalks and too many buildings, and didn’t have enough money to make it all nice, I’d choose to spend it the way Las Vegas does. It would not be a priority to fix all the pavement. We have choices about equity and we can choose between concrete and education.

The growing city as an engine of segregation and uniformity gives a person that city eye that believes it sees education when it sees nice concrete. Nice and safe and pretty and educated are supposed to go together, and dirty, crumbling, dangerous and desperate are supposed to go together. But those are false choices; if the money is tight, we can choose education over concrete without having to have both.