Buried deep in the FAQ on http://umpmfaq.info/faq.html
was the answer to my question:

"Try the settings in Tools|Options|Feedback|Personalized
Feedback in the Account Register"

- quote -

By default, spending thermometers are displayed at the
bottom of the account registers. If you right-click on
any of these thermometers and choose "Do not display",
the thermometers disappear from all account registers, as
expected. However, it's not at all clear how to get the
thermometers back later. What's the trick to making them
visible under the account register again?

Thanks in advance for any help...