Step 6: Build carrying case, Sew handle.
Again, you may follow the diagram I've provided and find measurements on how to build the carrying box. Or you may choose to make your own, unique version, or improve upon my own. I modeled mine after various kinds of medical, patient monitoring devices.
I spliced an RCA cable in between the circuit and the sensor/chest strap (Steps 7 & 8) so that it can easily plug in and out of the box. I chose RCA cable because it's a simple way to have two stranded wires, packaged nicely with an easy to plug/unplug header. I slipped the RCA cable into a length of latex tubing, for aesthetic reasons.