As an alternative to RTCs or microcontrollers, devices with an RC, as opposed to crystal-based, oscillator can be used for these applications. Because there is no external clock source with this solution, the frequency of the oscillator and thus the timekeeping accuracy of the device is less accurate than crystal-based solutions due to semiconductor process variations. However, these applications generally do not require a tight tolerance for the purpose of elapsed time counting for warranty expiration or preventative maintenance, which is typically measured in months or years. For robustness, there is no comparison. Not requiring a crystal or battery makes the RC oscillator the solution of choice for harsh environments. Even though microcontrollers can be very low cost and flexible to precisely fit the needs of the application, code revisions would need to be tracked over the life of the product.