I use a Skutt hand held digital pyrometer to check the kiln temperature at each level.
Some kilns run hot on the bottom or top. You can make adjustments to your gas kiln to monitor this condition. In my electric kiln , I place pieces with a glaze that has a range ( i.e. 4-6) in those variable spots. The middle of my kiln seems to be the most predictable ( the "sweet " spot).
Clay King is currently having a sale on pyrometers. Nice to own one.