How do you check if your furniture is actually level?

I recently noticed that a table can look perfectly straight but still be slightly tilted. Do you usually check things like tables, desks, washing machines, or cabinets with a physical level, or do you use your phone?

I found TrueTilt, which lets you use your phone as a bubble level and angle measuring tool:

https://play.google.com/store/apps/details?id=com.cleveroad.truetilt

Has anyone tried using a phone for this? Is it accurate enough for everyday home projects?