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I use a Perform Aire brand for bracket racing. It give you direct readout of Density Altitude and then predicts ET based on your previous input of runs.
If you put in only good runs, it will be consistant and help you dial up or down more accurately than you will without it. That may help win more rounds.
There are 3 models in perform Aire. I use the middle price one. I see some used ones on this site in varoius brands like TAG for $200 or less that might be good buys if you check out the seller and the condition and upgrades.
Don't get the old ones that you have to read 3 gages and then put in info on a calculator to get your prediction. I have a friend who has one like that and it is harder to use.