Number fields are handy field types for not only collecting numerical data with an efficient mobile keyboard format but also for automating calculations in your form. The rule of thumb for number fields are to use them anytime the value collected will be used in a calculation field later in the form. If the field won't be used for a calculation, i.e. a zip code or a phone number, short text fields in the style of number will be best.
The number style will allow you to toggle Allow Decimals on or off whereas currency will default to two decimal places. If the values from these number fields are used in a Calculation field, the decimals can be configured between 0 and 6 in the calculation field settings.
Currency will also add a label, such as a dollar sign, to the field in the form. The specific currency sign will vary depending on your individual device settings.
Note: Currency sign is generally location-based. If you need your form to collect data in a different currency, try changing the location settings on your mobile device.
Both styles of number fields will allow you to set a numeric Minimum and Maximum, which will require users to input a value either above a certain amount or below. These can be used simultaneously to ensure that value is within a certain range.