I'm sorry for the inconvenience. Version 3.8.13 of in5 has a bug that affects the Viewer Display Zoom. Our developer said that the bug is caused by the fix in 3.8.13 for relative links in a scaled, scrolling document that weren't working properly on load. They modified the code so that the Viewer Display Zoom will scale. 
Here's how to add the modified code:
- Copy the code below
 - Export either by going to in5 > Export HTML5 with in5... or to in5 > Easy Export Wizard... and clicking the Advanced button
 - Go to the Resources section of the Export HTML5 with in5 dialog
 - Click the + button in the JavaScript section
 - Click the Paste code... button to paste the code from your clipboard
 - Click the Save and apply button
 - Select Append to Existing at the bottom of the JavaScript section
 - Click OK to export
 
function getCurrentScale(targ, zooming) {
    var targ = targ instanceof jQuery ? targ[0] : targ, $body = $('body');
    var zoom = useZoomToScale ? $(targ).css('zoom') : 1;
    if(zoom && zoom !== 1) return zoom;
    return zooming || $body.hasClass('zoomed') || $body.is('[data-scaled-to]') ? window.scaleFactor || new CSSMtx(window.getComputedStyle(targ).transform).a : 1;
}