Adobe DC Scaling not working on MacBook

I have Adobe DC on my macbook. I use it to scale architectural drawings so we can bid on jobs. The scaling feature will work sometimes, but not others. In the screen shots below you can see I am selecting .5 inches (1/2") = 1ft or 12 inches. The scale should mark 29 inches for the area I am measuring. 

I have MacBigSur 11.2.3 installed on my Macbook. 

Please advise,

Juan