@JeanineB007
Project only allows one setting for defining a "day". By default, that is 8 hours which dovetails with the Standard calendar. If your plan has multiple calendars, some of which have a different number of hours in a "day", then there will be a disconnect when the Duration field is set to show days. Best practice for that scenario is to specify all durations in hours, then it doesn't matter what calendar is applicable.
However in your case, if you need to show summary lines in days while performance tasks are all in hours, and you have different calendars applied, then the custom field formula approach can still work but it will need to be modified to account for the hours in a "day" as defined for the applicable calendar. The custom field formula I gave you assumes a Standard calendar throughout with a normal 8 hour (480 minute) workday. If the summary line represents tasks that have a 24 hour calendar, then the divisor in the formula needs to be 1440, the number of minutes in a 24 hour "day". However, if the summary line is for a mixture of tasks with different work days, then a custom field formula won't produce a valid "day" value.
If your plan has a mixture of summary lines, some with all performance tasks on the Standard calendar and some with all performance tasks on a 24 hour calendar, then the custom field formula needs to be further modified to apply the appropriate divisor to the correct summary line.
It can get complicated in a hurry 🙂
If you want me to help further I'll need at least a screen shot of your plan showing a couple of summary line groups of tasks.
John
