Chandra Shekhar Chauhan

Yes, it is true that Capability Matrices (Cp & Cpk) are more relevant for manufacturing Industries where it is common to get 2 sided specification limits. These indices do not adequately address the issue of process centering. Foe addressing this issue, an alternative definition of Cp advocated by Taguchi. Taguchi introduced the name Cpm for the Taguchi Index and examined statistical properties of an inefficient estimator under the assumption that the process mean coincides with the target value. 
Cpm is now another interesting process capability metric that is not very popular. In fact it is more robust than Cpk. Cpm is an advanced measure and it corrects some deficiencies in Cpk. It is also called as Taguchi Capability Measure. 
 
We can easily understood the difference between Cpk and Cpm with this below Illustration and formula; 
Cpk 

 
Cpk is considered as a measure of the process centering for any process. If we closely observe the Cpk formula, it does not require the actual target value. target value is the center value obtained from the customer Given or design specification. However it takes the LSL, USL & Process mean. In this way, we can say that this is an indirect method of assessing if the process centered to the tolerance. 
In the above picture, in order to know if the plane is landing exactly on the middle of the landing strip, we look at the distance of the plane's nose from either edge of the strip. That is good but it's only an indirect way of assessing the process center. 
 
Cpm

If we look at the above picture and formula of Cpm, it contains the target value. Thus in addition to obtaining the USL and LSL from the customer or Design, we also obtain the Target Value. This means, Cpm is a true process capability index, because it compares the difference between process mean and target Value. To draw an image for plane landing, we are comparing the plane's nose to the median line of the strip. 
 
Lets take an example, where there is only a specification on one side. In most business processes, service levels have only an upper or lower specification. In some cases, Cpk losses its significance. However, in all service scenarios, there is a target value. For example, Customers are told that payment will be updated in 4 hours but the internal target is to get it done in 2 hours. Process is designed for 2 hours. In such scenarios, Cpm will be a relevant centering metric. 
 

 
In this scenario, Cpk is high, but Cpm 0.54 is very less value as comparison to Cpk 21.40. Here Cpm is very sensitive and good capability measure while Cpk is not. 
 
To get some hands on experience, lets calculate the value of Cpk and Cpm for another service industry; 

 
Below are the few examples of use of Cpm (Taguchi Capability Measure) in Service Industry, where we generally have one sided specification with Target Value; 
- Resolution time less than X hours 
- Call time less than X minutes 
- Payment update in less than X hours 
- Number of min order places per hours 
- Number of max. calls in waiting and so on ......... 
 

Network Diagram : 
Network Diagrams mainly are 2 types - Activity on arrow (AoA) and activity on node (AoN) are being used to analyze various tasks involved for completing any project, especially when it is being used most to the time that is required to complete each task and the minimum amount of the time that is required to complete the entire project. It is well known method which comes under the Program Evaluation and Review Technique called as PERT. 
There are 3 stages involved in developing a network diagrams are; 
- Planning stage 
- Sequencing stage 
- Scheduling stage 
 
AoA - Activity on Arrow 
It use arrows to represent activities while nodes stand for events.
Each nodes contains 3 numerical values : 
* Start time 
* Finish Time 
* Float or Slack 
AoA diagrams show the finish to start relationships with a limited offer like Arrow represents the time span from the event at the start of the arrow to the event at the end. Activities that are represented as arrows have to be added to illustrate some of the more complicated relationships and dependencies that are present between the activities. 
Such diagrams used dummy activity to show the relationship among various dependencies and dummy activity need Zero time to complete it. 
AoN - Activity on Node
Each activity is represented by Arrow with nodes at each end to represent the Start and Finish of the activity. 
In AoN diagrams, the activity is placed on the node. The interconnection arrows would illustrate the dependencies that are there between the activities. They are more flexible and are capable of illustrating the main relationship types. Since the activity is on node the data usually can be placed on the activity. 
Such diagram usually start from Start Node and end with the End node. And generally dummy activity is not being used. 
We can easily understand the difference between AoA and AoN diagram with this example; 

 


So what should we use?
While there are some fundamental differences between AoA and AoN network diagrams, choosing one over the other is based on individual project requirements and some time matter of the personal choice. Some of the basic differences would be as follows.
AoA networks were more popular in the 1960s and 70s. 
AoN focus on Task while AoA focus on Events.
AoN diagrams are generally easier to Create as compared to AoA diagrams. 
AoA shows only finish to start relationship, while AoN can show any type of relationship like finish to start, finish to finish, start to start, start to finish. 
AoN is widely used network diagram technique and supported by most of the project management software's.