I noticed that too. Sadly, my lcd is not fast enough to do double time like yours can though. Using the crystal timers, as they are more accurate, mine refreshes at 61.4 hz, and my max lcd speed from spedTest is 120. So you can see the problem there. Whereas, yours refreshes at 67.4 and your screen can handle 219. You could even go for the third pass, but that wouldn't actually be grayscale. :)

But technically that shouldn't make a difference. Doubling just makes the calculator load a completely useless frame in between the ones that are displayed. I don't see how that would take the lines away. It would also require 2/3 of your processor time and >100% of mine.

Edit:
   Post 100. Yay!!!!

Alright, here is the program that will tell me all I need to know. The more people that run this one, the better people will be able to make grayscale games in the future. You will also experience flickerless grayscale! with an occasional glitch line.

Just run gray4, press plus and minus to adjust the delay, and when you finally get the scrolling line to stop, (or come close), you will have the info that I need. So press second and tell me what you got.

And to avoid any secrecy, the Driver number is what I sent to port $29 to fix the lcd, (alcdfix), and Refresh is the value I am sending to port $32 with port $30 set to $40 (10922.667 hz). I am hoping that the different values sent to $29 will be enough to tell the different drivers apart so that the specific delay for each one can be used.

Oh, and wiki ti was perfectly correct.

Edit:
    I use 178 for mine. Doing a little bit of proportions, you should need about 163. Also, my delay is 44, yours is probably in the teens.

22.5 degree accuracy is really nice once you get the hang of it. In all reality, you probably only need to wait one frame to see if the other key is going to be pressed.

Mmmm.. That's harder than it sounds. I assume you have never needed alcdfix before then?

Before I incorporate it into the program we need to find your refresh rate.

Run this program. Keep pressing - until the image slows down and stops, or at least comes close. If you found the right spot, it will be one image and it won't repeat itself. You will also know you found it because it will slowly work it's way down to where it stops, it won't just stop all at once.

Once you found it, press / and it will tell you a number. Mine is 153. So yours should be around there. If you happen to find one in the 70s, skip it because it is double the refresh rate.

Then run spedTest because I have to know your cpu speed. Refresh runs too fast for the crystal timers.

Results are in. Grayscale looks better when you update by rows instead of columns. When you update by column, there is a diagonal glitch that is always scrolling on the screen. But when you update by row, it goes off screen and stays off for about 3/4 of it's cycle.

The lcd definitely updates from top to bottom. When I updated from bottom to top, I noticed that there were two glitch lines instead of one, when I switched to updating top down. There was only one glitch line that went off screen for a few seconds.

But I must say my 8 level viewer looks really nice. Here is the program with some test pics so you can see how it looks. It's easiest to see what I am talking about in gradient.

I'm not sure, I'm currently writing an 8 level grayscaler. Doing it that way, there wouldn't be a diagonal line, I just wonder what the cross over point would look like then. Maybe there wouldn't be one if you're lucky.

Also, I think you would have to start at the bottom and work up, because I feel that's how the lcd is updated. But I'm not positive.

Well since this topic was originally about 16 level grayscale, let me share some facts that I just figured out.

I thought, well maybe I can get 64 levels out of it by putting one pixels on in the first column, two in the second, three in the third, and so on until the 64th column is completely full. I then changed the z-address to scroll the screen 100,000 times per second. (For those who don't know, the z-address is where the lcd driver starts to display at, so if you set it to 1, the very top row of pixels appears at the bottom and all others scroll up one, a 2 does the same except by two pixels.) The z-addressing is nice because it only takes one command to update the entire lcd. But this didn't work at all and I got these weird scrolling patterns. So then I thought, I'll figure out the refresh rate.

I made a refresh rate program. Through careful tweaking I found that at 3,811 z-addresses per second made a perfectly still image. So every 1/3,811 of a second, the driver displays another line. Divide this by 64 and the screen refreshes at 59.5 hz.

What does this mean, this means that if your grayscale program updates the lcd faster than 59.5 hz, it won't make a difference. My 16 level just happens to update it 120 times per second. I suppose this means that within a few hours I will have an 8 level grayscale viewer instead.

I included an example to show you how perfect the grayscale looks when you update the lcd at the right speed. This is a weird version of tetrisM I am working on. If your driver updates at 59.5 hz, you will see 100% flickerless grayscale with a little slant the scrolls through the screen.

Next update. Again, all improvements are seen in the screen shot.

I can't believe it, but the game is basically done. Probably just a few level tweaks and that's it.

And I would have 100% in both levels.