You can use a watch with a dive bezel to track two timezones at onces without a GMT hand. This works because dive bezels typically have markers for every 5 minutes and, since time is base 12, you can calculate the second timezone with simple division.
How does it work?
Turn the dive bezel so that the nib is on the timezone offset hour marker. For example, if you are on Pacific time and you also want to track Eastern time, rotate the bezel so the nib so is on the 3 o’clock marker.
To read the time in the second timezone, look at the hour hand to find the hour marker (as usual), find the corresponding minute located on the dive bezel, then divide by 5. Read the minutes as normal and you have the hour and minutes of the second timezone!