In the Mid 1970s, When I was working for Manning Vally Floorcoverings in Taree, N.S.W.,-

Clive Norling  (the Owner) asked me If I could do a demonstration in the shop to show customers how to D.I.Y. Rubber-backed carpets. Rubber-backed Carpets were popular as ‘Kitchen Carpet’ at the time.

Clive had just bought a heap of end-of rolls of a particularly cheap but trendy carpet. 
Rubber backs were easier to lay as they did not require stretching, tacking or fastening. 
At the time, we had a good portion of customers who liked the idea of a soft kitchen floor. So I said Yes! (I’ll try anything once)  Most of our rubber-backed carpets had a thin backing layer of black rubber. In no time, I realised that the simple method of running a piece of white chalk around the room’s perimeter (generally  Kitchens) ensured a heavy chalk deposit at the base of the wall and floor. Simply Running A brickies, bolster held hard against the edge of the carpet and transformed the chalk line to the back of the carpet.

The old bolster was merely a tool that  I had handyI had handy at the time, But it was heavy and worked a treat.