Excel tries to be helpful by setting the cell format automatically based on what you type in the cell; for example, if you type 2 2/3 then the cell’s value is set to 2.66666666666667 and its format is changed to show as a fraction.
There are a few quirks worth noting.
If you use a built-in function that returns a percentage then the cell will be automatically formatted as a percentage. For example, =RATE(12,-10,100) is converted to a percentage and displayed as 3%. However, =RATE(12,-10,100)*2 is not converted, so displays as 0.058457082.
Other functions are more forgiving; for example =TODAY()+1 is automatically formatted as a date.
If you type a currency string that is recognised as such by Excel then it is converted automatically. This depends on what your regional settings are set to in Windows.
With British settings £3 and €4 are both converted to currencies, but $5 remains as a string. With US settings, only $5 is converted.
My guess is that the reason that all currencies are not converted automatically, regardless of the regional options, is that some symbols are used for more than one country and Excel needs to pick a particular variant.
Date strings are automatically converted, but again (and this is a good thing) depend on the regional options.
Get to the point...
The main point of this posting is to state that if you are writing instructions for Excel users you must make sure that their regional options are the same as yours unless you want strange things to happen.