As mention by Nesa this is not achieved with Simplified Field Notation because this built-in feature is limited to only four basic mathematical operators.
You won't be able to establish a "less than" or "greater than" comparisson using this method in Acrobat as you would with electronic spreadsheets.
In the same context, even though you can employ a custom calculation script to achieve a comparisson between the values or the properties of the desired fields, this method is not exclusively necessary.
The easiest way to achieve this is to use the built-in "Value is the" calculation option.
For example, in the "OfficeUseActualAssetsAvailable" field, select or tick the radio button "Value is the" and select from the adjacent dropdown menu "minimum". Then click on the adjacent "Pick..." button and tick the checkboxes for the fields: "OfficeUseActualAssetsAvailable" and "TargetAssets".
Conversely, do the same procedure in the "NameOfBox" field, but choose "maximum" from the dropdown menu, and then check the fields: "NameOfBox" and "TargetAssets".
This built-in feature will, in a way, establish a comparisson between the values entered in the fields.
For example, if a user types in a number value in the "NameOfBox" field that is less than the value of the "TargetAssets" field, it will default back to the value of the "TargetAssets" field, but it will accept a number value that is greater.