From what I have seen, TTS DataMaster is the way to go. It is light years ahead of Diacom. Go to the Diacom website.... it was Popular Mechanics "Product of the Year" in
1991!!!!..... the dark ages. It is an antiquated DOS-based program, with a ridiculous price. I think if you want the limited graphing capabilities, you need the Diacom "Plus" or something like that, which is around $500. Not recommended, unless you have a stable of 1985-1995 GM cars of various brands that need a lot of scanning. DataMaster is limted to the OBD-I LT1.
They also misspell the name of the product as "Diatom" on one page......

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DataMaster does have some features that aid you in diagnosing problems, or at least interpreting the data. On the BLM's for example, it will color code the cells that are deviating from normal, to indicate the magnitude of deviation. The only thing I have found odd in some of the data logs that people have sent me to look at is the numbers it produces for injector duty cycle... they just look way too high for the power some of these engines are making.
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Fred
94 Formula A3: 381/TH400/N2O
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11.513@115.59 on motor; 11.162@127.67, 1.643 60' on a 125-shot. Going with a 275-shot this year