This belonged to my Dad and is probably from the 70's or 80's. I want to find a new home for it (if it is still useful) but I don't know what it is exactly. It appears to be some sort of steadying support which you wear but i'm not sure
This appears to be a SLIK EZ HOLD chestpod.
Details online are very scarce, so I would presume the model has been discontinued, but the central column is very similar to the current line of SLIK Easi-pod monopods. The manufacturer may have more information about the chestpod if you need its specifications.
I could not find any images of the SLIK chestpod in use, but the design is not dissimilar to this one by Novoflex which may give a clearer idea of how the parts would be positioned in use.