Half built kiln walls

Today the 18th row, pictured here, was mortared.
The middle peep hole is barely visible in the back wall through the doorway.

I've patched holes in the 3 rows of foundation bricks that were seeping sand. Sand had been swept between the bricks of the 3 bottom courses to keep the bricks from moving. But it kept slipping out - I guess as the earth rotates, it shakes the sand down, or something like that. Perhaps, as I walked on the kiln floor, it shook the sand through.

I'm feeling like I'm making progress. I can tell the walls are getting higher because it is hard for me to read my tape measure across the top. I placed cinder blocks along the front & back, so I can reach the top easier. It will be the next row or two that I'll have to use a stepladder.
Just as I am picking up time in my bricklaying technique, I'll be moving slower as I tote a stepladder around.
If I was taller and could see the top of the row I'm working on, I would just have to lay more rows. I'm going to make the kiln just tall enough for me to stand up inside. That will make it easier to set kiln shelves when loading pots for firing.

Measuring:
After placing the inside hard bricks for each row, I measure across each direction on the inside. Need to make sure the walls are even & parallel. As every brick is mortared, each measurement is double checked with the tape measure & a level. Before setting a brick the place is swept with a small hand broom, and the brick itself is swept. Only then can the brick be mortared.
Also, the diagonal measurement across inside corners is checked, so it stays the same from the bottom to the top of the kiln.
Today I learned how to use a 4' level vertically and see how straight the walls are. Sounds easy, but as with many things there are tricks/techniques to reading the tool properly. If I'm making it sound like there is something to it, it is because I was doing it wrong, and needed to be shown the correct way. I guess I'm saying that when I think something should be easy, sometimes I find I'm doing it all wrong - as I did with this. Now I know how to check the verticality of each corner.

Enough for today...