Question 1

What pressure should my car tyres be?

Accepted Answer

Check the placard inside the driver’s door or the handbook, since it varies by vehicle and load. Most British cars sit between 30 and 35 psi, which is roughly 2.1 to 2.4 bar or 207 to 241 kPa.

Question 2

What is the difference between a millibar and a hectopascal?

Accepted Answer

Nothing at all. Both equal 100 pascals. Meteorologists adopted the hectopascal when SI units were standardised, but the numbers on a weather chart did not change, which is why older British forecasts and newer ones read alike.

Question 3

Why is blood pressure measured in millimetres of mercury?

Accepted Answer

Early sphygmomanometers were mercury columns, and a reading was literally the height the mercury rose. The instruments have changed but the unit was kept so that a century of clinical records remain directly comparable.

Question 4

What does a boiler pressure of 200 psi mean in modern units?

Accepted Answer

About 13.8 bar, or 1,379 kPa. Late Victorian express locomotives typically ran boilers between 175 and 225 psi, a figure that rose steadily as steel fabrication improved through the nineteenth century.

Question 5

What is feet of water used for?

Accepted Answer

It expresses hydraulic head, the pressure produced by a column of water of a given height. A tank thirty feet above a tap delivers thirty feet of water, or about 13 psi, which is why Victorian engineers reasoned in the unit directly.

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