However, note that costs are always calculated on an hourly basis,
regardless of the units used to display work or the way the standard rate is
entered. If I have a resource whose rate is entered as "$100/day" and I
assign him to a task that runs from 9am to 11am on Monday, if the "Work"
field is formatted to show days it will display "0.25 day" and the cost will
show $25.00. It's up to you to figure out something else for him to do that
day as well in order to get your money's worth of the full $100 you have to
pay him to show up at all and if you don't include that other work in the
project, Project won't count the additional $75 in the cost.