Resource Histograms (Edexcel A Level Further Maths) : Revision Note

Constructing a Resource Histogram

What is a resource histogram?

• A resource histogram is a graphical way of showing the number of resources needed during each time unit (e.g. day) of a project

•  A 'resource' usually refers to a person (called a worker) but could refer to

  • a team of workers (e.g.  bricklayers, roofers, painters)

  • a machine (e.g.  cement mixer)  

• The number of workers needed will vary as a project progresses and will be determined by

  • the activities that need to happen at a particular time

  • the number of workers needed per activity

• A resource histogram shows at a glance the maximum (and minimum) number of workers/resources needed for a project

• Resource histograms can be used to help minimise the number of workers at any particular time during a project

What assumptions are made in drawing a resource histogram?

• In the first instance, there are three main assumptions used in order to construct a resource histogram

  • Each activity begins at its earliest event time

  • A worker/resource can only carry out one activity at a time

  • Once an activity has begun, it must be completed in one go e.g.  If an activity C, say, of duration 5 days, starts on day 7, it has to take place on days 7, 8, 9, 10, 11 It cannot be done on days 7, 8, 12, 13, 14  for example

• Once a resource histogram is constructed, the assumptions can be reconsidered

  • This may be so that the number of workers/resources required at any given time is minimised

    • This process is called resource levelling and is covered in the next revision note

How do I draw a resource histogram?

• The horizontal axis is used for time

  • However units of time are treated as discrete data

  • So "day 1" would be labelled underneath the first column 

• The vertical axis is used for the number of resources (number of workers)

• For each unit of time

  • a box per worker is drawn with a label of the activity that worker is doing

  • multiple boxes are 'stacked' on top of each other

    • critical activities are at the bottom of the stack

    • other activities appear in alphabetical order

• Each activity commences at its earliest event time