In modern-day sash windows, you might be far more more likely to look for a spring harmony (or sash harmony) system. This is a spring-loaded device which counters the drive of gravity, in outcome Keeping your sash window open without the need for cords, pulleys and people metal counterweights.  Here https://bathroomandkitchentilingl20585.bloggactif.com/36900690/how-sash-windows-can-save-you-time-stress-and-money