Vcc is 5V

R1 is 3.3K, R2 is 6.8K

My usual approach is to reduce the parallel portions of the circuit and simplify, so that I can calculate the total impedance and then the current, then the voltage drops/voltages at each nodes.

The above circuit slightly simplified:

And again:

So from this point my understanding of theory fails me. I can only arrive at the correct (measured at 7.4K) value by totally ignoring R1, calculating:

(R2 + R2) in parallel with (R2 + R3), i.e.

R4 in parallel with R5, i.e.

13.6K in parallel with 16.9K = 7.54k!

This is the closest I can calculate to the measured value, however of course R1 is missing. I'd greatly appreciate any help and theory corrections.

Regards.