Different pitch harps same key

David, 

Hope all is well. I got an tuner app called Soundcorset and used it to compare the 4 blow on my three A harps. I tested each by closing my eyes and playing each harp 3 times in order to ensure a fair reading. Each was somewhat off. I’ve emailed screenshots of the three results. The Manji is the most acurate, while the SP20 is middle and the Rocket the sharpest. 

Do you have any explanation for this phenomenon? FWIW, the app calibrates A4=440Hz.