Renter here in a 1960's home. (I'm the one with loose electric outlets.)

I have my gas hot water heater set on the arrow which I assume is average
hot. When I shower, I don't turn on any cold water. In other words, just the
hot water on is ok for a shower. If I'm feeling like a real hot shower, I'd
have to decide the night before and turn up the water heater.

Is this normal? Do you think this could be due to sediment? I don't think
the heater is older than 10 years but it's not a real efficient one. It's in
my heated basement and I put a "blanket" on it a month ago, hopefully to
save a bit of money.

Should I just turn it up to "A", "B" or "C"...which I assume is hotter since
it's up the dial. I don't want to waste money.

Thanks,
bonnie