Modern weighbridges are designed for high accuracy, typically within a small margin of error. Here are some factors that influence accuracy:  

• Calibration:Regular calibration using certified test weights is crucial. Well-maintained weighbridges with frequent calibration can achieve accuracies within 0.1% to 0.5% of the actual weight.  
• Maintenance:Proper maintenance, including cleaning, lubrication, and repairs, is essential to ensure consistent accuracy.  
• Environmental Factors:Temperature fluctuations, wind, and vibration can slightly affect readings.  
• Operator Skill:Proper vehicle positioning and data entry by the operator are important for accurate results.
• Weighbridge Type:Different types of weighbridges (e.g., platform, in-motion) may have varying levels of accuracy.  

I guess you might also want to read the article about Beyond the Scale: Exploring Weighbridge Applications, Varieties, and Processes.