Here's my review (of sorts) of the Micro MinimOSD, something you can put on your 250 and more usefully use it to mess about with your PID settings.
I like it a lot, despite managing to blow one up (but that's my fault)
Some links from the video -
Here's where you can get the OSD (affiliate link) -
The excellent MWOSD firmware
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...and don't forget the FAQ (I hit two problems that were covered in this, but I ended up in the main docs directory in Github and missed it)
Here's Oscar Liang's excellent blog
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...and this is the link to his document about setting up the micro
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