Before the baizes with the roulette wheel neighbour layout were produced, casinos in the UK used neighbour (marker) buttons which were placed on the wheel rim with the button on top of the stake which could be time consuming especially if many were used during the game as you had a "container" that you had to put them all back into before the next spin. It also led to a few no spins due to them falling into the wheel if called during the spin so the layout printed ones did make life a lot easier for the croupier, especially the clumsier ones.
In some London casinos the maximums were £3000-£5000 on a number and the full complete marker was placed onto the (relevant number on the) layout with the stake underneath. Obviously if a part complete won they left the marker there and either placed the bet (taking away the stake) or just paid it whilst including the stake that would have been placed if done the other way. They also catered for inside completes (which just meant no outside part, streets and six lines) which were used in the same way.
All of the high end casinos expect staff to know their full/part completes inside out (parrot fashion) but there are many "tricks" to working them out too.