A perfect correlation is denoted by a correlation coefficient of 1.0 or -1.0. A correlation coefficient of 1.0 indicates a perfect positive correlation, meaning that as one variable increases, the other variable also increases at the same rate. A correlation coefficient of -1.0 indicates a perfect negative correlation, meaning that as one variable increases, the other variable decreases at the same rate. In both cases, the variables are perfectly related, meaning that the relationship between them is linear and there is no deviation from the relationship.