This field allows you to indicate what all measurements for this Measurement Type will thereafter be assumed to be if you do not specify otherwise.
It is suggested that your Default Unit is a unit of measure that you most frequently enter measurements as this will save you having to enter the unit each time.
For example, if you enter 19h 14d 30w (instead of 19cm h x 14cm d x 30cm w), the system must make an assumption about what you have entered, and it will do so based on what you specify in this field.
If you frequently enter measurement data in different units of measure (e.g. if the nature of your data means you sometimes enter measurements in inches and sometimes in centimetres) you can create separate Measurement Types to facilitate this. For example you can create a Measurement Type called 'Dimensions (Metric)'.
You can always override an assumed unit of measure by simply entering a different one when you enter the Measurement Reading. For example even if you have specified Centimetres as the Default Input Unit, you can enter 19 x 4 x 3in in the Measurement Reading field and the system would accept this, and would convert the measurement to your specified display unit.
The assumed unit is different from the display unit. The display unit you specify tells the system how you want measurements displayed, regardless of the way they were entered. For example, you can enter a measurement in inches or centimetres and it will always be displayed as inches if that is the display unit you have specified.
The assumed unit of measure tells the system what a measurement is if no unit is entered with it, and has no effect on how measurements are displayed. For example you could indicate that measurements should be assumed to be centimetres unless otherwise specified, but that you want them displayed in inches. This might be a useful thing to do if the data you have been supplied with is all in centimetres, but your institution uses inches - i.e. by indicating Centimetres as the Assumed Unit you can enter measurements quickly, without having to type the 'cm' for each one, but these will then be converted and displayed as inches.
