Truly MP3 13X only showing blue backlight

I found how to set the date and time on my Truly DB61M blood pressure monitor by trial and error. I suspect other Truly BP monitors do it a similar way. These monitors also seem to go under the name Accuread. It's a pity they don't make manuals readily available online.

Here's how you do it:
1. Put the monitor into the date/time setting mode by holding down the MEMO and AVG buttons together for several seconds, then release.
2. The YEAR will be displayed flashing at the top right of the display. Press the PAGE button to move through the years to the one you want.
3. Press the AVG key to move to the next field, which is the month, flashing on the left. As with the year, used the PAGE button to move through the months to the one you want.
4. Following the same procedure, set the day of the month, the hours and minutes. The monitor knows how many days are in each month, so you can't set eg 31 February.
5. To finish, press the START button (the one on the right with the red marking).
There seem to be some other settings as well as the date/time that come up if you keep pressing the AVG button, but I don't know what they are.