Cost Entry Mode
Mandrel provides two different ways in which you can express cost uncertainty when you enter cost data:
Costs are entered in terms of a base cost plus a contingency. For example, $1000 + 10% contingency implies that you expect to spend $1000, and, depending on circumstances, may spend up to an extra 10%. Of course, if you know the exact cost, the contingency can be zero.
Costs are entered in terms of a base amount with variances. For example, $1000 +20% -10% means that you think the cost will be somewhere around $1000, but are not sure of the exact amount. In this case the cost has been expressed as a range which is equivalent to ‘somewhere between $900 and $1200’.
Any cost item can be in either mode at any time. You can freely switch between modes.
Every cost element in Mandrel is stored as three separate values, a base or mid-range cost, a positive variance and a negative variance, e.g. $1000 +20% -10%. The negative variance (-10% in this example) is simply ignored in base+contingency mode.
Which Mode Should I Use?
High/mid/low generally represents a greater level of uncertainty than base+contingency. Typically, you would start in high/mid/low mode for an uncertain cost and switch to base+contingency when the cost becomes firmer. For less uncertain costs you can use base+contingency mode from the outset.