In this part, the following conventions are used:
 The abbreviation “F” is an indication for safety related items, technologies, systems, and units (failsafe, functional safe).
 The default data that are used in case of unit failures or errors, are called failsafe substitute Values (FSV) and are set to binary “0”.
 Reserved bit (“res”) are set to “0” and ignored by the receiver for avoiding problems with future versions of OPC UA Safety.
 Terms and names are often written in PascalCase (the practice of writing compound words or phrases in which the elements are joined without spaces, with each element's initial letter capitalized within the compound). Terms or names where two capital letters of abbreviations are in sequence or for separation to a suffix are written with underscores in between.
 The notation 0x… represents a hexadecimal value.
Requirements in this document are designated as [RQx.yz], where x denotes the chapter number, y is a counter and z is an optional character to link closely related requirements. The following are examples of valid requirements designations: [RQ8.15] (requirement 15 in chapter 8); [RQ47.11a], [RQ47.11b] (requirements 11a and 11b in chapter 47, which are closely related).
The initial numbering of requirements was chosen such that counters within each chapter are in ascending order. However, the addition of further requirements leads to deviations from this rule since existing requirements shall keep their initial designation.
For an informative list of all the requirements in this document, see Clause C.2
 [RQ3.1] Any CRC signature calculation shall start with a preset value of “1”.
 [RQ3.2] Any CRC signature calculation resulting in a “0” value, shall use the value “1” instead.
 [RQ3.3] SPDUs with all values (incl. CRC signature) being zero shall be ignored by the receiver (SafetyConsumer and SafetyProvider).
Table 1 – Conventions used in state machines
Convention 
Meaning 
:= 
Assignment: value of an item on the left is replaced by value of the item on the right. 
< 
Less than: a logical condition yielding TRUE if and only if an item on the left is less than the item on the right. 
<= 
Less or equal than: a logical condition yielding TRUE if and only if an item on the left is less or equal than the item on the right. 
> 
Greater than: a logical condition yielding TRUE if and only if the item on the left is greater than the item on the right. 
>= 
Greater or equal than: a logical condition yielding TRUE if and only if the item on the left is greater or equal than the item on the right. 
== 
Equality: a logical condition yielding TRUE if and only if the item on the left is equal to an item on the right. 
<> 
Inequality: a logical condition yielding TRUE if and only if the item on the left is not equal to an item on the right. 
&& 
Logical “AND” (Operation on binary values or results) 
 
Logical “OR” (Operation on binary values or results) 

Logical “XOR” (Operation on binary values or digital values) 
[..] 
UML Guard condition, if and only if the guard is TRUE the respective transition is enabled 