# Incorporating Cycle-Time into Your Model

This section presents a process for incorporating cycle-time into your models. At its essence, the process is quite simple. The process involves four basic steps, as outlined below:

1. Determine the "starting line" in a conserved flow chain.

2. Time-stamp the flow(s) which represent the starting line.

3. Determine the "finish line" in the conserved flow chain.

4. Tap into the flow associated with the finish line using a connector and converter. Define the converter using one of the cycle-time Builtin functions.

Let's take a closer look at each step in the process.

1. Determine the starting line: In this step, you're deciding what flow(s) in the process should be considered as the starting line, for the purpose of generating cycle-time metrics. Any flows in a conserved flow chain can be used as the starting line. In Figure 10-2, for example, one could choose from among many potential starting lines. Any flows downstream from the starting line you choose can be used for the generation of cycle-time metrics.

Figure 10-2 Choosing a "Starting Line"

Thus, if you identified the flows enter queue 1 and enter queue 2 as the starting lines, you then could collect cycle-time data such as the wait time for process 1, the total time for process 1, and the cycle-time for the overall process. If, on the other hand, you decided to use enter process 3 as your starting line, the associated cycle-time calculation would apply to Process 3 only.

Notes:

- When you have multiple entry points to a main chain, you will want to consider making each entry point a "starting line." In Figure 10-2, if enter queue 1 is designated as the starting line but enter queue 2 is not, only the material which moves through the main chain via enter queue 1 will be considered in the subsequent cycle-time calculation.

- It's possible to designate successive stages in a main chain as starting lines. In Figure 10-2, for example, you might want to designate both enter process 1 and enter process 3 as starting lines. However, if both flows are time-stamped, material that moves through enter process 1 will be time-stamped again, when it moves through enter process 3. This material will lose its earlier time-stamping.

2. Time-stamp the flows which represent the starting line: To time-stamp a flow, begin by entering the flow's define dialog. As indicated in Figure 10-3, you'll find a check box next to a small stopwatch icon at the top-right of the dialog. This check box is the time-stamping check box. Check the box. Then, click OK. When you return to the diagram, the flow's appearance will change to indicate that it has been time-stamped. An illustrative time-stamped flow is also shown in Figure 10-3.

Figure 10-3 Time-Stamping a Flow

3. Determine the "finish line": The finish line is the point in the conserved-flow chain where you want to collect the cycle-time information. As shown in Figure 10-4, the finish line can be any flow which is downstream of the starting line in the chain. There must be a time-stamped flow upstream in the conserved flow chain, if cycle-time calculations are to have meaning.

Figure 10-4 Choosing a "Finish Line"

4. Tap into the flow associated with the finish line: To wrap up your work, you'll use a connector and a converter to tap into the finish line flow. In the modeling mode, you can define the converter using one of the cycle-time Builtin functions. As illustrated in Figure 10-5, this step is straightforward. When you exit the converter's define dialog, the converter will sport a partially-filled clock face. This is your visual indication that the converter is generating cycle-time data. When you subsequently run your model, as the time-stamped flow volume crosses the finish line its time-stamp will be used to generate the desired cycle-time data.

Figure 10-5 Tapping into a Downstream Flow

Notes:

- It's possible to tap into a conserved flow chain in multiple places, so as to collect cycle-time information from multiple-stages in a conserved-flow chain. Each metric will be generated based upon the closest upstream time-stamp.

- By using multiple converters tapped into the same downstream flow, you can calculate a number of different cycle-time metrics at the same point in a process.

- Cycle-time Builtins are available only in converters. They will be gray unless the converter is tapped into a flow in a conserved flow chain, and you have time-stamped a flow somewhere upstream in the same conserved flow chain.