The look of a field tells you what it expects, and the same signals are used throughout the system:

What you see | What it means {class="compact"}
---|---
A small arrow at the end of the line | A list to choose from. Free text is not accepted here — if the entry you need is missing, it has to be created in the configuration first.
A field showing `0` | A number is expected, and one is always required. Leaving it empty is not the same as zero.
A date field | Filled from the calendar or by typing — see [Working with the calendar](/General-Usage/working-with-calendar.md).
A time field | Entered as `hh:mm` in the 24-hour clock.
Everything else | Free text.

## Fields that have to be filled

Which fields are mandatory is decided by the configuration and differs per module and per category. A record that refuses to save usually says which field is missing — that message names the field as it appears on screen.

Two cases are worth knowing, because they look like faults and are not:

* **A field is missing entirely.** It is switched off for this module or category, not broken.
* **A field is greyed out.** The record is in a state that no longer allows changes — closed, approved, or open for reading only because it belongs to a closed process.

*[PO]: Purchase Order  
*[AZA]: local folder
*[(PO]: Purchase Order  
*[RQ]: Requisition  
*[(RQ]: Requisition  
*[RfQ]: Request for Quotation  
*[(RfQ]: Request for Quotation  
*[SO]: Service Order  
*[(SO]: Service Order  
*[SQ]: Service Requisition  
*[(SQ]: Service Requisition  
*[SRfQ]: Service Request for Quotation  
*[OoB]: Open on Board  
*[(OoB]: Open on Board 
*[ART]: Average Running Time (operation hours per day) 
*[MC]: Master Contract
*[ADS]: Advantage Database Server (database engine used in previous versions of the ZeeBORN software)
*[.replic]: file extension for replication files (aka data transfer files)