I assume that you’re talking about a Superchart, as opposed to the now redundant Graph widget?
I think you’re saying that you’ve set the gauge widget display properties to be one decimal place and used the same virtual pin as a data stream in Superchart? If that’s the case then I don’t think the gauge decimal place display has any effect on the number of decimal places used in the Superchart.
You probably need to format your data in your code before sending it to Blynk.
You don’t say which type of MCU you’re using (or for that matter any of the information that you’re prompted to supply when you create a new thread), but if you’re using an ESP8266 based device then ther was an issue with decimal places when using an earlier version of the ESP Core. I think that issue worked the other way around, truncating decimal places rather than preserving them, but it would be a good idea to ensure that you’re up to date with the latest ESP core (if that’s the hardware you’re using) and Blynk library.