A sash cord is the rope that passes over the axle pulleys used to hang the sashes, counterbalanced by the sash weights. While a Sash weight is a cast iron or lead weight, a pair of which counterbalance the weight of each sash.
With the requirement for restoration on sash frames. The cord and weight could also be in need of some care. What’s great about sash windows built in the 18th & 19th century, is that these can often be found intact with a high degree of strength and rigidity. Therefore it’s advised that these windows are investigated, as simple restoration work could see the wood and other materials last for many more decades, perhaps centuries.
The restoration of sash windows is where we could also encounter the issue of rotting sash cords. Which requires another replacement. The re-balancing of sash weights may also be required. Not only do you reduce the risk of damage, but the movement of the lower and upper sash windows will become much smoother.
Much like the function of a sash weight. A make weight essentially provides further weight to support the sash box. The requirement for make-weight can occur should the lower and higher sash boxes be fitted with glazing units for restoration purposes for example, meaning the original weight can no longer support these new sash boxes.