Comparing the # of records to the # of days in a duration.

I have a table that is for "jobs", which has a one to many relationship with the "daily job updates" table. I have a formula - duration field on the "jobs" table for the # of days that a job was in progress. I also have a # of daily job updates field as a summary field in the "jobs" table. 

In practice, for every day that a job is in progress there should be a daily job update. So at the end of the job, the # of days in progress and the # of daily job updates should be the same.

I need a report that tells me how many jobs didn't meet this criteria and how many daily job updates were missed. My thoughts were to just make a formula - checkbox in the background that if( ([# of days in progress] - [# of daily job updates])>0, true, false), and then a formula - numeric that is just [# of days in progress] - [# of daily job updates] to list on the actual report drilldown.

Is this the best way to do this, or am I going the more difficult route?