cross reference fix

Author: TorkelE

docs/src/model_simulation/examples/activation_time_distribution_measurement.md

@@ -28,7 +28,7 @@ plot(esol)
 ```
 Here we see how, after the input time, the system (randomly) switches from the inactive state to the active one (several examples of this, bistability-based, activation have been studied in the literature, both in models and experiments[^1][^2]).
 
-Next, we wish to measure the distribution of these activation times. First we will create a [callback](@ref https://docs.sciml.ai/DiffEqDocs/stable/features/callback_functions/) which terminates the simulation once it has reached a threshold. This both ensures that we do not have to expend unnecessary computer time on the simulation after its activation, and also enables us to measure the activation time as the final time point of the simulation. Here we will use a [discrete callback](https://docs.sciml.ai/DiffEqDocs/stable/features/callback_functions/#SciMLBase.DiscreteCallback) (for an ODE simulation, a [continuous callback](https://docs.sciml.ai/DiffEqDocs/stable/features/callback_functions/#ContinuousCallback) would instead have been appropriate, however, these combine less well with stochastic models). By looking at the previous simulations, we determine $X = 100$ as a suitable activation threshold. We use the `terminate!` function to terminate the simulation once this value has been reached.
+Next, we wish to measure the distribution of these activation times. First we will create a [callback](https://docs.sciml.ai/DiffEqDocs/stable/features/callback_functions/) which terminates the simulation once it has reached a threshold. This both ensures that we do not have to expend unnecessary computer time on the simulation after its activation, and also enables us to measure the activation time as the final time point of the simulation. Here we will use a [discrete callback](https://docs.sciml.ai/DiffEqDocs/stable/features/callback_functions/#SciMLBase.DiscreteCallback). By looking at the previous simulations, we determine $X = 100$ as a suitable activation threshold. We use the `terminate!` function to terminate the simulation once this value has been reached.
 ```@example activation_time_distribution_measurement
 condition(u, t, integrator) = integrator[:X] > 100.0
 affect!(integrator) = terminate!(integrator)