Apple Watch ECG issue

When I try to take an ECG reading the watch responds with things like: keep your arm still, hold your finger on the crown. I am already doing those things, and am usually unable to take a reading. After researching online, here's what I found that works: clean the watch sensor and crown. be sure you have good posture when taking the reading- dont lean over. rest the arm on a table, and sometimes resting on a pillow helps keep the arm still. Those things have allowed me to get a more positive experience when using the app.