Parent Table: Deployment

Child Table: staff

Deployment has a lookup field (called related_staff) to select however which staff worked on a specific deployment. 

I need to report the number of staff who worked deployments at various points in time (monthly, quarterly, yearly, etc). First I need to know how many staff worked each deployment. I added a field on the Deployment table (called staff_count) and tried various deluge workflows, but I can not get it figured out. 

Thoughts?

Also, is the zoho creator chat service down? I click on it, and nothing happens.