Don:
In TCR computer file, we have a "letter" value column that is published. We also have averaged numerical value columns for TCR-3, TCR-4, TCR-5 & TCR-6 that are not published. We decided to use the (+) & (-) for TCR-5 to show an increase or decrease compared to TCR-4, only if the change was at least one letter level. If there was only a change within the letter level, e.g. from $15 to $18, there was no (+) or (-) shown.

We average the values from all auctions (Annual club, Herz, Richmond & Sones,
Chip-Chat, Gaming Times, Coast To Coast, Campiglia, Pfeander, etc. We see many sales lists (C.T. Rodgers, Scott Hartman, Gary Snover, Dave Harber, Walt Dirzulaitis, etc, etc, etc.) We get many phone calls, e-mail & snail mail from collectors with new buys, sells and finds.

In conclusion, those little +'s & -'s only show that a chip was at least one level higher or lower or stayed the same when compared to the previous edition.
Are they useful? I don't know. We try to add something new each edition & thought the added info might be interesting to some. Possibilities for the next edition are succession dates of all Nevada casinos at each address and scans of hard to I.D. chips such as large & small print, or bold & fine print. We try to improve each edition. The main improvment in TCR-5 was the updating of all 10,700 price values. We welcome all suggestions.