Consider encouraging volunteers to take breaks
I've done my first few pages of household review tonight, and it was more physically and mentally strenuous than I anticipated. This is significantly different from the direct transcription I'm used to when indexing.
I think FamilySearch should frequently encourage volunteers to take breaks.
Very few people's eyes are conditioned for the constant vertical saccades the household review task requires. Unless you play video games for a couple hours a day, you're probably not used to looking up and down continuously like this. This can cause real strain on your eye muscles.
There's additional mental strain from the lack of visual landmarks on a preprinted columnar form. Your brain has to keep track of which column and row it's on in two different places simultaneously. "Let's see, that's two blank fields, then an N, then three blanks, then 031, one blank and a G. Or was it three blanks then two? Wait did the bottom pane scroll down? Is this all on the wrong row?"
Every time a user finishes a household is a good opportunity for a break.
Give the user a little praise, then remind them that now's a good time to step away for a minute. Some users may feel guilty if they haven't finished a full page, and they absolutely shouldn't.
You'll want to vary the wording every time, too. If someone sees the same message in the same place 3 or 4 times in a row, they'll literally stop perceiving it's even there. If you can come up with 8 messages for praise and 8 messages for break encouragement, a random combination of them will seem fresh every time and will be more likely to actually get read. Take the rare opportunity you have here to make users smile.
Maybe commenters here can suggest some messages in the replies.
Praise: Great job! Your careful review will mean a lot to someone researching this family someday.
Praise: That's one household down, a few million more to go!
Praise: We're really grateful for the time you put into this project.
Encouragement: Now would be a great time to take a break. We'll still be here when you return.
Encouragement: What's the weather like outside? If you need a break, just let us know when you get back.
Encouragement: Could your eyes use a break after that last one? Your optometrist will thank you.