Rough calculation
A rough calculation is the term used to describe calculating with numbers that are strongly rounded up or down to quickly check complex calculations.
The rough calculation is a very imprecise method that only serves to check results for their credibility or to determine unknown mathematical values on the basis of already known mathematical values. Therefore one should be very careful with this method.
Examples of applications
Currency conversion
Many people use rough calculations in currency conversions, for example to compare a price in euros with an earlier currency.
In rough calculations with rounded factors (in Germany about 1: 2 instead of 1: 1.95583, in Austria 1:14 instead of 1: 13.7603) rounding errors occur, which affect the converted price (mostly the more significant currency depreciation since Introduction of the euro causes a major methodological error ).
| Exact calculation | → | Rough calculation |
|---|---|---|
| 1: 1.95583 | → | 1: 2 |
| 1000 euros = 1955.83 DM | → | 1000 euros = 2000 DM |
Slide rule
When calculating with slide rules, you had to calculate the position of the comma in a rough calculation, since the slide rule does not show the order of magnitude of a number.
Heating time of a water boiler
The specific heat capacity of water is 1.16 Wh / (kg K ). For a rough estimate or a rough calculation, the value 1 Wh / (kg K) is sufficient. In order to heat a kettle with 100 liters of water (approx. 100 kg, depending on the temperature) by 10 K, one needs roughly 1 kWh. A 30 kW gas burner needs "around 2 minutes" for this, a 10 kW burner "around 6 minutes". This gives results that are sufficient for an assessment. The more or less exact value to, for example, three decimal places is not necessary.