I always loved Wheelwright & Clark's chart, quote it all the time, though now it has to be 30 years old, but hammers home the point of how much damage over extending yourself or a team can be. I created a really crappy example to show the math, been almost 20 years, so I really should make a new one, but this one should work - though really ugly and confusing graphics. Add this to the list of decks I should make prettier when I have free time, but will be dead by then.

1. 1Jay Martin Month Year FileName.ppt
Date: November 2000
Presentation:
Jay Martin
Engineering Efficiency
Multi-Tasking
‘The Math Showing You Just
How Bad It Hurts You’

2. 2Jay Martin Month Year FileName.ppt
When deciding how many projects to work on, there are two major
conflicting beliefs with respect to what will yield the optimal results.
Engineering Efficiency Project Assignments – Two Schools of Thought
Though both have valid points, the following study done by the head
of Harvard Business School shows that the first one is incorrect.
Start every project as soon
as you get a chance.
• Everything gets started right
away
• Can show progress on all
activities
• Better prepared for changes
in priorities
• By starting right-away, you
will have more chance to
finish
• With more projects, your
time will be spent more
efficiently
Focus your efforts to best
maximize your efficiency.
• Less time cycling back and
forth in coordination
provides more value-added
time
• Too many projects become
unmanageable
• By focusing on fewer, you
complete the ones you start
first sooner
• More uninterrupted time on
projects allows for more
progression on deliverables
1 2

3. 3Jay Martin Month Year FileName.ppt
Engineering Productivity is optimized at two projects, and then
begins a dramatic downward slope as project number is increased.
Engineering Efficiency Productivity Chart
?
10
20
30
40
50
60
70
80
90
100 %
0 1 2 3 4 5 10
68 %
82 %
62 %
47 %
32 %
>10 % (est.)
Source: Wheelwright and Clark, Revolutionizing Product Development, Free Press, Chapter 4.
Note: Percentages not quoted in book (not exact), estimates based on graphical information.
Productivity of Development Engineering Time
Percent of time
dedicated to
value-added
work
Number of Projects Assigned Concurrently to a Single Engineer

4. 4Jay Martin Month Year FileName.ppt
Using the information on the previous page, we created an example to
show how it is better in both efficiency and schedule completion.
Engineering Efficiency Example
Scenario 1 Four 3 man-month projects, one person, all started concurrently
Scenario 2 Four 3 man-month projects, one person, started 2 at a time
A
B
C
D
Completion
All projects
completed at 25.5
months after start
date.
Total time spent was
25.5 man-months.
A
Completion
Projects A & B
completed at 7.3
months and Projects
C & D completed at
14.6 months.
Total time spent was
14.6 man-months.
C
B D
J F M A M J J A S O N D J F M A M J J A S O N D
J F M A M J J A S O N D J F M A M J J A S O N D J
100 %
100 %
0 %
0 %
50 %
50 %
25 %
75 %

5. 5Jay Martin Month Year FileName.ppt
An analysis of the math better explains this concept and its value.
Engineering Efficiency The Math
Scenario 1 Four at once
Scenario 2 Two at a time
Completion
All projects
completed at 25.5
months after start
date.
Total time spent was
25.5 man-months.
Completion
Projects A & B
completed at 7.3
months and Projects
C & D completed at
14.6 months.
Total time spent was
14.6 man-months.
• All projects start at month one.
• With four projects, we will have an
efficiency rating of 47 %* value-
added.
• Each of the four projects requires 3
man-months of value-added.
• Total man-hours of work required to
complete all four projects = 25.5
(4 projects)(3 man-months)/(47%)
• In the previous equation, you are
multiplying the number of projects by
work required (to get total work), then
dividing by the efficiency.
• Assuming all projects were needed
ASAP, then another interesting value
would be the delinquency to completion
for the entire set of projects; summation
of complete dates = 102 total months
(Complete A)+(Complete B)+(Complete
C)+(Complete D) =4(25.5)=102
• Two projects started at month one
and then two more immediately
after their completion date.
• At two projects, the efficiency rating
will be 82 % value-added.
• Each of the four projects requires 3
man-months of value-added.
• Total man-hours of work required to
complete all four projects = 14.6
2*(2 projects)(3 man-months)/(82%)
• An easier way to compare in the future
is to use the efficiencies against each
other to estimate the impact (.82/.47)
• To continue the emphasis as to why this
scenario is better, we again want to
show how having the first two completed
sooner supports this; the summation of
complete dates = 43.8 total months
(Complete A)+(Complete B) + (Complete
C)+(Complete D)
=2(7.3)+2(14.6)=14.6+29.2= 43.8
* See values from graph two pages back