Why?
The elimination of the excess of the imbalance of small cards (+ Value Red 7's) combined with the proper IRC serves to accomplish the same thing as a true count conversion. Assuming an IRC of -12 for a six deck game using Red 7...
Some comparisons of High Low +2 True Counts at Different Deck Levels to the same Red 7 Running counts in a six deck game. Note 0 (Zero) is both the Pivot and Key Count in Red 7 or the point where you go from making small bets to larger bets and where you always have the most accurate measure of your advantage. For most players using High-Low +2 is where we begin to make our first real bets as well. (advantage 0.5%)
5 decks to go
High Low RC +10, Red 7 RC +0
4 decks to go
High Low RC +8, Red 7 RC +0
3 decks to go
High Low RC +6, Red 7 RC +0
2 decks to go
High Low RC +4, Red 7 RC +0
1 deck to go
High Low RC +2, Red 7 RC +0
Now, doing the same exercise...this time for High-Low +1 True Counts
5 decks to go
High Low RC +5, Red 7 RC -5
4 decks to go
High Low RC +4, Red 7 RC -4
3 decks to go
high Low RC +3, Red 7 RC -3
2 decks to go
High Low RC +2, Red 7 RC -2
1 deck to go
High Low RC +1, Red 7 RC -1
So you can say a Red 7 count of exactly 0 will equate always to a High Low count of +2 or roughly 0.5% advantage. Above and below 0 the High-Low equiv depends on how far into the shoe you are. Since nobody wants to remember 5 different sets of betting ramps they just simplify and use one that gets most of the value when you reach the "meat" of the shoe. This means most players will say that -3 Red 7 Running roughly equates to +1 High Low and that will be most accurate with 3 decks to go. That means you may miss some small advantage opportunities early in the shoe but these aren't where most of your money is to be made.
So,
High Low TC.....Red 7 RC
-1 -9
+0 -6
+1 -3
+2 0
+3 +3
+4 +6
+5 +9
I've found the biggest headache is figuring a wongout point for unbalanced counts. I would wong out at -18 early in the shoe and -12 late in the shoe and -15 in the middle of the shoe.