A method, device and system for representing numbers in a computer including storing a floating-point number M in a computer memory; representing the floating-point number M as an interval with lower and upper bounds A and B when it is accessed by using at least two floating-point numbers in the memory; and then representing M as an interval with lower and upper bounds A and B when it is used in a calculation by using at least three floating-point numbers in the memory. Calculations are performed using the interval and when the data is written back to the memory it may be stored as an interval if the size of the interval is significant, i.e. larger than a first threshold value. A warning regarding the suspect accuracy of any data stored as an interval may be issued if the interval is too large, i.e. larger than a second threshold value.