Consistency

Example: Fire Extinguisher

Photo source: CTF 3, Unimas

Figure 4.3.1 shows a fire extinguisher

• Aesthetic Consistency

Aesthetic consistency refers to consistency in terms of physical outlook, like style and appearance.
Fire extinguisher exhibits great consistency in terms of designs. They are said to have aesthetic consistency as the style and appearance of a fire extinguisher is the same everywhere. Most fire extinguishers are either in bright red or blue, making it easily recognizable from afar. Hence aesthetic consistency in fire extinguishers is important to make it easily noticeable especially during an emergency. 

• Functional Consistency

Functional consistency refers to consistency in meaning and action such that people are able to use their existing knowledge to know how things function.
Fire extinguishers exhibit functional consistency as fire extinguishers are designed to have big levers. The big lever on fire extinguishers which affords pushing has make use of the user's existing knowledge so that users will automatically know how to press the lever to extinguish fires even if they have never use one before .It is crucial to have functional consistency as users would not have the time to read the instructions during an emergency if fire extinguishers operate differently from one another.

• Internal Consistency

Internal consistency refers to consistency within the design itself in the system.
Fire extinguisher has internal consistency as fire extinguishers are standardized in every part of the world. All fire extinguishers operate the same everywhere, which is to pull the pin, aim at the fire and squeeze the lever. They also have the same cylindrical shape, making it more mobile and easier to move.

• External Consistency

Figure 4.3.2 shows fire hose.

Figure 4.3.3 shows fire reels.

External consistency refers to consistency with other element in the environment that has similar functionality.

Fire extinguishers exhibit external consistency. The nozzle and hose of a fire extinguisher is the same as the nozzle and hose of fire hose (seen in Figure 4.3.2) and fire reels (seen in Figure 4.3.3)  used by firemen. These firefighting equipments are also consistent in terms of colours. They are usually in bright red colours to attract attention.