I was going to say something about the first blue marker being hard to see - but I think you've already worked that one out. The subsequent markers were absolutely fine.
The next thing is that there was a bit of echo in the audio. It wan't much and there wasn't a problem understanding you, but I did notice. There are a couple of ways of dealing with this. Getting closer to the microphone is one - but sometimes that isn't practical, for example if you are using an on camera mic. Another way is to hang something that absorbs sound - such as curtains. If you want to try this, start by having a single drop covering part of one of the reflective surfaces (usually walls) that is reflecting sound into the microphone. The amplitude of sound reflections can be reduced by moving further away from the reflecting surfaces - but if you have a limited lab space (as most do) this isn't going to be possible.
However - this is NOT a big thing, so don't lose any sleep over it. You can still do videos like this and everyone will be able to hear.
One last thing - which, again, is not a big deal - is lighting. The illumination on the whiteboard was very good throughout ... we could see it clearly, but your face was in shadow on occasions. Having some better illumination of your face wouldn't hurt, IMO. It need not be a light, just having a plain white surface behind the camera to reflect some of the room light would probably be enough. This might also bring up the whiteboard a little better, too.
AGAIN, this is no big thing. I am being picky. What you are doing is more than good enough to keep going - so don't let these comments slow you down!