Co-ordinate Crosshairs with constant readout on interactive map

Hi everyone
a new iteration of Valles Marineris interactive map built with Hype and Chart.js plus some custom code I built to show a smooth crosshair for identifying Longitude/Latitude coordinates giving a constant readout. Click to fix position of crosshairs, then further click and move cursor to change position - its quite intuitive. Needs to be viewed on desktop preferably....minimum of 1200px width.