Calculating the age of the universe is accurate only if the assumptions built into the models being used to estimate it are also accurate. This is referred to as strong priors and essentially involves stripping the potential errors in other parts of the model to render the accuracy of actual observational data directly into the concluded result. This is not a valid procedure in all contexts, as noted in the accompanying caveat: "on the assumption that the project's underlying model is correct". The age given is thus accurate to the specified error, since this represents the error in the instrument used to gather the raw data input into the model.