An instrument system that includes an elongate body, a first optical fiber, a second optical fiber, and a controller is provided. The first optical fiber is operatively coupled to the elongate body and has a first strain sensor provided on the first optical fiber. The second optical fiber is not directly coupled to the elongate body and has a second strain sensor provided on the second optical fiber. The controller is operatively coupled to the first optical fiber and to the second optical fiber. The controller is adapted to receive a first signal from the first strain sensor and to receive a second signal from the second strain sensor. The first optical fiber has a different size than the second optical fiber.