problem calculating the difference between two duration fields.

[Henk]

Hello project experts,

When I am copying one duration field to another to calculate the
difference there appears a problem.

e.g. the field copying the field "remaining work" to "duration 1" and
then calculating the difference results in values like

T1 0.02
T2 -0.03
T3 0.02
T4 0
T5 0.03

Though I would expect all to be exactly zero.

What helps to solve this?

Best regards, Henk

 

[John]

Hello project experts,

When I am copying one duration field to another to calculate the
difference there appears a problem.

e.g. the field copying the field "remaining work" to "duration 1" and
then calculating the difference results in values like

T1 0.02
T2 -0.03
T3 0.02
T4 0
T5 0.03

Though I would expect all to be exactly zero.

What helps to solve this?

Best regards, Henk

Henk,
First, I have no idea what your values T1, T2, etc. represent. Second,
how are you calculating the difference? Third, Project handles all time
related values to the nearest tenth of a minute so it is possible the
values you think you are seeing are actually rounded values. Hence the
difference may not in fact be zero.

John
Project MVP

 

[Jack Dahlgren]

This is rounding error.
If I am remembering correctly, work is stored in a different unit (tenths of
minutes?) than duration is (minutes). Converting from one with more
precision to one with less precision will create a rounding error unless you
are really lucky. I'd not use duration1 and use a number or text field
instead.

-Jack Dahlgren
http://zo-d.com/blog

 

[Steve House]

In addition to John's comment, work and duration are not in the same units
or even measuring the same thing and so are not directly interchangeable.
Though both are commonly referred to by "hours," work is correctly referred
to as "man-hours," a unit measuring the expenditure of energy similar to the
'kilowatt-hour" used for electricity, while duration "hours" truly are units
of time.