You CAN change the volume on the FT-1D with one hand if you perform the following.
1. Go to setup (hold in DISP button)
2. TX/RX (ENT)
3. Audio (ENT)
4. Volume Mode (ENT)
5. Select AUTO BACK
Now you can adjust the volume with just one hand by pressing MUTE first and then turn the knob. You no longer have to hold the MUTE button down.
This has always been a pet peeve of mine with this radio. Until now, it was not very user friendly to change the volume while driving.
**** UPDATE – Link to video is here.