Here is a free thinkscript for everyone looking to include Market Internals in their Think or Swim platform.
You can tweek your centerline but the default is 1.
#---------------------------------------------------------------begin of Script
declare lower;
input show_NYSE = {"No", default "Yes"};
input show_NASDAQ = {"No", default "Yes"};
input centerline = 1;
plot uv = if(show_NYSE, (close("$UVOL") / close("$DVOL")), double.nan);
plot dv = if(show_NYSE, (close("$DVOL") / close("$UVOL")), double.nan);
plot nasu = if(show_NASDAQ, (close("$UVOL/Q") / close("$DVOL/Q")), double.nan);
plot nasd = if(show_NASDAQ, (close("$DVOL/Q") / close("$UVOL/Q")), double.nan);
plot center_line = centerline;
uv.SetDefaultColor(Color.GREEN);
dv.SetDefaultColor(Color.RED);
nasu.SetDefaultColor(Color.CYAN);
nasd.SetDefaultColor(Color.GRAY);
#---------------------------------------------------------------end of Script
http://www.investopedia.com/terms/b/breadthofmarkettheory.asp
