I had a running pi 3 with node-red on it and for various reasons I wanted to re-install the OS. Backed up the flows and re-installed the latest raspbian image 2020-02-13 buster and re-installed node-red using the script
bash <(curl -sL https://raw.githubusercontent.com/node-red/linux-installers/master/deb/update-nodejs-and-nodered)
when I run the flow I get the output that looks like this.
I get the NaN output as shown in the image.