The one requirement for making this work is that you must always type the units of the numbers you enter. For instance, when entering the length of something into an equation, you may not enter "12" but must specify the units like so: "12 m" or "12 in". A number without a unit is interpretted as dimensionless, which is sometimes its own dimension! (For instance, if you must enter an angle, and you merely type "π", Math Touch will assume "π radians") Always enter units afer typing a number, i.e. type "12 in" not "in 12". Any precisions or imaginary values must also be entered before the unit names.

For more information about how Math Touch performs dimensional analysis, recognizes units, the warnings Math Touch will give you for errors, or how you can modify the database of units, see the appropriate subsections below:

Dimensional Analysis

The Unit Database

Unit & Dimension Warnings

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Values are sometimes entered as a combination of other units. For instance, acceleration due to gravity at the Earth's surface is approximately "9.812 m/s^2". The carrot ("^") indicates a power, which in general will be an integer. Entering this text exactly as shown here will work, and there are also special characters to enter the superscript 2 power.

Regarding the division symbol, there are two caveats: 1) it is not necessary to separate the division symbol "/" with spaces from units names, and 2) the division symbol may be used only once for each value, entirely separating the units in the nominator on the left, from the units in the denominator on the right. For instance, "1.57 m kg/s s" would be recognized identical to "1.57 m kg s^-2", not a reduced "1.57 m kg". When displaying such unit values, Math Touch always uses a division symbol to display such composite units, and always lists each unit symbol only once, using a superscript to indicate a non-unity power. This is not exactly the standard form in science, but is generally more convenient to read in limited space.

In version 1, Math Touch does not perform math function when entering values, nor does it allow mixed unit notation. I.e., you may not enter "2 m + 1 in" , nor "5 lb 3 oz", nor "5º 2'". Such notations work at different purposes to Math Touch's main objective. The "2 m + 1 in" example would require "interpretation" which is not allowed on the iPhone, and the "5 lb 3 oz" is would technically be multiplication, which is not the user's intent.

If you enter a name, plural or symbol that has been already used, Math Touch will refuse to allow it, since unique text is the only way Math Touch is able to recognize units you enter. This means that all of your symbols must have a unique name and symbol.

Here are the rules for new and modified unit names, symbols and plurals. 1) Names, symbols and plurals may not begin with numbers or math operators, such as -, +, ^, ±, /, !, or ., and they may not contain any superscript number or character. Numerical multipliers such as "π", "∞" and "i" as unit names may cause confusion with numbers and should be avoided as first characters. 2) All names, symbols, and plurals must not conflict with any other unit's name, symbol or plural. Differing in capatalization only is allowed. For instance, "c" and "C" would be allowed as unique symbols. A single unit may use the same text as its name, symbol and plural, but this is only seldom useful. 3) Symbols may not contain spaces. While names and plurals may contain spaces, hyphens are the suggested substitute. Math Touch will read units you type by splitting them at the spaces, so when a unit name contains a space, it will never be recognized. You may not use mathematical operators besides the hyphen-minus, such as "+", "/", ".". 4) While subscript 0 is available, other subscripts are not supported. 5) While most unicode characters are supported, the iPhone's keyboards may limit the characters you can use. Use the special keyboard to use some common characters the iPhone's regular keyboard does not support.

There are two preferences related to preferred units. The first is the unit system. If you prefer "SI" or "English" or "cgs" units, you may select your preference in the "Preferences" item in the information menu (the "i" menu). Simply select the system name you prefer, and all future calcualted units will be converted to the preferred unit in the appropriate dimension.

The second preference is for each dimension. In each unit system, each dimension has a preferred unit. To change the preferred unit in a particular dimension, go to the definition of the unit in the unit database, and edit it. Tap the "Set as Preffered Unit in System button," which will bring up a list of unit system names and the corresponding preferred unit name in each system. Select the system or systems in which you would like to set the current unit as the preferred unit.

Finally, any time a value is calculated, a unit conversion button appears next to it, you may tap this button and type in the units you prefer to see the value instantly converted.

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