What is the difference between additional information plate 8.1.1 ('300 m') and plate 8.2.1 ('↑ 300 m ↑') installed below a warning sign?

1. Plate 8.1.1 indicates the width of the road, while 8.2.1 indicates vehicle height.
2. Plate 8.1.1 indicates the distance from the sign to the start of the hazardous section, while 8.2.1 indicates the total length of the hazardous zone.
3. Plate 8.1.1 applies to passenger cars, while 8.2.1 applies to freight trucks.
4. Plate 8.1.1 indicates daytime validity, while 8.2.1 indicates nighttime validity.