I did an informal survey of control buttons:

<Lichess, chess.com, Fritz 12, CB Light 2009, Chessbase db online, Chessbase site (their new viewer), NIC online, CT, 365, and RHP>

and nobody uses "+". All have symmetric forward/backward controls, and many (well, all, really) use a variant of ▶ for autoplay.

A couple other things specific to mobile use:

The play buttons are very small for big clumsy thumbs and I find myself regularly clicking move 3 or 4 just below the play button and then (because I don't know what move number I was on due to the previously mentioned problem) I have to go searching for where I was in the game. Hassle!

Also, and I don't know if this can be corrected, especially early in the game I'm clicking through a known opening quickly and invariably the screen size blows up, a reaction to a "double tap" I suppose. It happens all the time. Hassle!

*scroll, scroll*
Tap settings, whoops! so tiny and close to engine link, accidentally tapped engine, opened up a new window, had to close that window, back to original game window, Tap settings
Tap flip board

With pgn4web:

<I like the movement of the pieces but the control board below is crude and dated in design.> By control board, do you mean the left/right/etc. arrows or the "settings box"? In either case I agree they look a bit crude, but that can be tweaked with CSS styling.

<It's disconcerting not having the move and move number visible right below the board, as pgn4web has it.> Sorry, I didn't mean to be vague: originally I wanted that info out of the way, because things like "Black is in check" is not something that a good chess player needs to be informed about. But the more I use the software the more I think it's a good idea to have the move number and previous-move visible without scrolling, and the "status" info of the game can come along for the ride. Exactly where to squeeze it in without creating unnecessary white space will have to be explored.

<Oddly sized buttons> Somebody asked why the buttons are not all exactly the same size (and others will surely ask again) — it was an intentional design decision to make the most commonly used buttons (notably "forward move") bigger than the others. On desktops I personally use → and ← to scan through the games but on mobile devices you have no keyboard, so I wanted the ">" button to be the biggest one available, taking up 40% of the button space. In experimentation this makes misclicks much less likely.

<Auto-zoom> As to the topic of clicking buttons so fast you trigger you mobile OS "zoom in" feature, we're well aware of this issue. I'm not quite sure, but I fear there is nothing that can be done about that. It seems to manifest on iOS more than Android. I've already learned to avoid the problem by timing my clicks just a little slower than the OS recognizes.

<nobody uses "+"> Except for pgn4web and Olga. <Lichess, chess.com, Fritz 12, CB Light 2009, Chessbase db online, Chessbase site (their new viewer), NIC online, CT, 365, and RHP> ... <I actually took notes, and suggest CG do a similar study. ... many (well, all, really) use a variant of ▶ for autoplay.>

We did in fact do a survey but our results seem to contradict yours. Mind sharing your notes? We saw that most of them do not <use a variant of ▶ for autoplay> but rather don't offer the autoplay feature whatsoever. Where is the autoplay feature on Chess365, Lichess, NIC online, Chessbase Online, or Chessbase's new viewer? Do they hide them with hot-keys? I certainly don't see a button for that purpose on any of those viewers but I don't use those products so perhaps I missed something. RedHotPawn simply has a button that reads "Play" but as an international product we tried to avoid English labeled buttons.

Thanks, it is. It was working again so quickly I wondered whether I had got it wrong. Wouldn't be the first time. Thanks for acknowledging also.

On another tack, I see another member has said "I don't like the wiggly move" (for want of a better phrase), and "please remove it".

My view on these things is to ask "why not both?"

I dislike it a lot. But I can see that others may like it, so why not a toggle button/check box to switch it on or off?

PS- Here's the PGN viewer control comparison notes I made... well sort of:

https://zanchess.wordpress.com/2017...

I turned it into a Visual Puzzle to have a little fun while doing the work of making it presentable.

But I couldn't get to it easily yesterday, since somebody had changed my default viewer. Ha!

<A simple suggestion: add a button to inject your Stockfish analysis straight into a post eliminating the need for any intermediary copying and pasting.>

On a mobile phone I can't hit 'f', so that won't work for flipping the board. Is that the function key you mean?

Some changes I would want before i considered switching from pgn4web: Easy method to flip board (valid for mobile)
Ability to turn off the annoying continuous piece movement. Ability to change autoplay speed.

If not please let me know your platform (device, OS, browser).>

When I saw this I immediately thought "rounding error" for calculating the pixel location of the path of the piece, as it now clear this feature isn't a deliberate choice of coding. You mention the possibility of rounding error later. I'm viewing this in Firefox. I'd be surprised if it is browser-dependent, but I've not tried another browser so can't say from my end.

Re: the board staying at the reset size from the default. It did for a short while, but today on opening chessgames.com its back to the same default size. I resized it down, switched to another game in the notes (two Carlsen games, the second linked in the notes, not that it should matter), and it reset to the default size on changing games.

So I agree- there's a bug in the code for calculating the path of the piece, and there seems to be a second bug in the code for tracking when a user resets the size of the board. The bar with the settings also moves with the resetting of the board size (implying screen location of the settings bar is linked to the board location), which isn't how I would do it- I would have the settings panel to the side of the board, and fixed on screen once it is opened. Having to move to a new location each time the board size changes to click the "change board size" icon (since it appears you can only do this incrementally, rather than from a drop down choice or dialog box for entering the size), to offering a list of possible sizes to choose to (example: drop down list of font sizes) might also be something you want to fix.

Some experimentation indicated that it happens when the ratio has been affected (zoomed in or out) and yes, probably is a 1-pixel round off issue. I don't understand why some people always experience it; I have to really try to coax it into that behavior by changing scale. By the descriptions I wonder if some people experience it worse than others. I find the 1-pixel wiggle almost cute, but if it was 2-4 pixels it would look ridiculous.

One idea to ameliorate the issue is to allow a mode where piece animations are turned off entirely. If they "blinked" from one square to another they would not wiggle.

We know that on some mobiles/tablets if you click a button too fast you can activate "zoom" -- but that's true for nearly every website on earth. My advice: just slow down.

Yes, 'f' only works if you have a keyboard. The tablet/mobile approach is the settings. The only other alternative would be to add a new main control button.

Speaking of the control buttons, we'd like to make them bigger (taller) and perhaps find better icons. Note that they change size with your browser text size.