The key is Fluidity. Elasticity. Flow.
Checkpoints can be helpful.
But try to look beyond checkpoints and observe muscular tension and smoothness of stroke.
Follow Chris at these websites and social media links:
Website: www.chrislewit.com
Blog: www.ProdigyMaker.com
Facebook: www.facebook.com/ChrisLewitTennisAcademy
Twitter: www.twitter.com/chrislewit
LinkedIn: www.linkedin.com/company/chris-lewit-tennis-academy
Instagram: www.instagram.com/chrislewittennis/
YouTube: www.youtube.com/ChrisLewit
iTunes: https://podcasts.apple.com/us/podcast/the-prodigy-maker-tennis-show/