問題：
Why does Math work differently between my older TDS200 or TDS1000/2000 series oscilloscope+ and my newer TDS1000B/2000B series oscilloscope?
答案：
The way to calculate math was different in the older TDS200 and TDS1000/2000 series oscilloscopes then most other oscilloscopes, including the new TDS1000B/2000B series.
The older instruments used a method that could be called Display Math. In Display math, the math is done on the screen values of the signals, in other words, in divisions. So if you had two signals that were the same voltage value, but one was scaled differently, you will get a different math result then if they are at the same scale. For example:
Figure 1: Channel 1 and 2 are both two divisions tall, so Math is 0.
Figure 2: Channel 1 is now 1 division tall, so Math is now 1 division.
Most of our other oscilloscope do math using a method called Data Math. This math is done on the actual data value, rather then the value displayed on the screen. No matter what scale you have the channels, you will always get the same math values. For example:
Figure 3: Channel 1 and Channel 2 are both 20V, so Math is 0V
Figure 4: Channel 1 and Channel 2 are still both 20V, so Math is still 0V
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