This app is bloody brilliant for helping you to calculate your exposuretime when using black glass.

This app is bloody brilliant for helping you to calculate your exposure time when using black glass. Of course there are others out there (I've used most of them) but this one is SIMPLE. Well done LEE Filters

I don't care if you're using Lee, Singh-Ray, or Formatt Hitech you're going to find this app useful in calculating your exposure times.

You can find it for Android on the Playstore
https://play.google.com/store/apps/details?id=com.leefilters.admin.leestopperapp

And ios in the App Store
https://itunes.apple.com/au/app/lee-filters-stopper-exposure/id1105022698?mt=8