# Calc FAQ

## Miscellaneous Questions

Q: Why am I getting 743559489.4000000059 instead of 743559489.4?

A: This problem should be solved in the current release of Calc (version 5).

Q: Why do you get (e.g.) 12.3499999999999943 if the display precision is set to 16 digits, but 12.35 for 12 digits?

A: Although it is possible to set the accuracy to 16 digits on older versions of Calc, the floating point unit does not support this precision. In the current version of Calc the maximum precision is 15 digits, and most of the rounding problems have been resolved.

Q: If I put in 19.4, it changes that to 19.3999999999999985. Why?

A: This can happen with older versions of Calc if you set precision to 16 decimals in fixed point mode. In the current version of Calc the maximum precision is 15 digits, and most of the rounding problems have been resolved.

Q: Is Calc capable of doing fractions?

A: Fraction mode is available in version 5.6 onwards.

Q: Why don't you have a scrolling tape?

A: This is the most requested enhancement for Calc. We have so far hesitated to add this feature because it is difficult to reconcile, from a usability point of view, with a scientific calculator with matrix functions. We hope very much to find a solution to this and add this feature to Calc at some future date.

Q: Can Calc calculate exchange rates?

A: If you know the current exchange rate you can of course do the conversion just like any other calculator. It is not so easy to simply add exchange rates to Calc's data files, however, because obviously exchange rates are constantly fluctuating (with the exception of periodically fixed exchange rates such as certain European currencies which are linked to the Euro). The exchange rates built into the properties database are those prevailing at the date indicated.

Q: How do I bring up the Periodic Table of Elements?

A: In version 5.3 you need to click on the "cnst" button to bring up the constants dialog. Then click on the "Elements" button. From version 5.6 onwards it is accessible from the "Tools" menu.

Q: How would I calculate a percentage of change?

A: Example 1: In 2004 you have an investment worth \$237 and in 2005 you it is worth \$376.
Solution: 376 - 237 = / 237 % ('%' key otained by using shift button). Result: 58.65%

Example 2: In 2004 you have an investment worth \$237 and in 2005 you it is worth \$182.
Solution: 182 - 237 = / 237 % Result: -23.21%

The extra '=' is required to make sure the subtraction is completed before the division.

Q: Why is a Calc's keypad upside down when compared with a telephone keypad?

A: The bottom row of Calc's keypad is numbered 123 with 456 and 789 above, like all calculators. A telephone keypad has 123 at the top with 456 below and 789 below that. In both cases the zero and other buttons are on the bottom row.

In around 1960 the telephone companies apparently arrived at their keypad layout as a result of useability research. It probably also made more sense to run the numbers top to bottom because of the alphabetic groups (1=ABC, 2=DEF, etc.) which would suggest reading left to right and top to bottom.

The early mechanical adding machines had a set of number buttons for each digit, e.g. the comptometer, and these ran from 0 (if used) or 1 at the bottom to 9 at the top. This was probably easiest for the design of the adding mechanism. When the first "ten key" calculators were manufactured they probably just extended the same convention for the smaller keypad. As usually happens with these things, once the standard is established there is no incentive for anybody to change.

Some people have suggested that the telephone companies deliberately made their keypad difficult to use so that the exchange could keep up, but this seems very unlikely to be true.

Q: Why doesn't Calc have a conversion from teaspoons etc. to ounces?

A: This question crops in many forms, in which a conversion is needed between a measure of volume and a measure of mass. Cups, teaspoons, fluid ounces, pints, litres and cubic feet are all measures of volume, whereas ounces, pounds and kilogrammes are measures of weight (or more strictly mass). Because they are different properties there is no direct conversion; it depends on the density of the substance. For example flour has a typical density of about 600 kg/cu.m, or 0.6 times that of water. From this you can do the conversion. But this density will vary with the type of flour and how it is stored and handled. In many cases a more practical solution is to weigh the container before and after filling to determine the equivalent weight.

Q: Why is your value for conversion to Btu incorrect?

A: There are a number of different conversion factors for the British Thermal Unit depending on the situation. This is because the definition of the Btu is the amount of energy required to raise the temperature of a pound of water by one degree Fahrenheit. This is dependent on the temperature and pressure (usually assumed to be atmospheric) of the water. To convert to other units of energy you need to specify the temperature, hence the different conversion factors. The variation with temperature is small, and can be neglected for many practical calculations, but it is enough to give slightly different converted values. The default conversion in Calc is a good approximation for typical working conditions, but in each particular industry the adopted conversion factor may be different and this should be used instead. You can add these to the conversion factors in Calc's conversion data if they are not already included.

Q: How do I calculate the rate of compound interest?

A: There is no built-in function to recover the compound interest rate for a given principal and return. However it can be calculated by taking the nth root of the ratio of the future value (FV) divided by the present value (PV) and subtracting one. Multiply by 100 to give the percentage rate. Here, n is the number of periods (e.g. years if working with annual rates and calculations of interest). Example: If an investment of \$100 today results in a return of \$150 in 3 years, what is the compound annual interest rate? 150 / 100 =; take the cube root (shift button, then the power/root button, then enter 3); = - 1 = x 100 =; result: 14.47%.

Q: How do I calculate a logarithm to a base other than 10 or e?

A: To get the log to any base, n, we recommend taking the log (to base 10) and dividing by log(n). Example: to take log to base 2 of 8 : 8 log / 2 log = (result: 3)

Q: Is the degrees API/Baume conversion correct?

A: Unfortunately there is not a straightforward conversion between Degrees API, as a measure of specific gravity, and other measures of density. This involves a reciprocal set of units and an offset. An incorrect conversion is included in earlier versions of Calc - please do not use the deg API or deg Baume conversions in Calc versions 5.3 or earlier. In later versions of Calc it has been removed.