This paper proposes a cryptographic mechanism for metering the duration and/or the number of instances of running a data process. This mechanism has the following property: knowing a secret, one can validate a piece of metering evidence in constant units of time while without the secret the job of generating a valid piece of evidence requires time indicated by a value in the evidence. Because the mechanism utilises a well-known computational complexity problem, the meter based on it can be implemented in software yet is tamper-resistant. We will address the use of this mechanism in building an auditable metering scheme for finding the popularity of web sites. The scheme is suitable for rapidly increasing web advertisement applications. We will also discuss the related security issues and mention some other applications, which can benefit by using the mechanism.