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Why is Maxima replying with there inaccuracies:
(%i1) kB : 1.38x10^-23;
(%i2) Ng1ppmFactor : 1e-6;
1.38*10^-23 cannot be represented exactly as a (binary) floating-point number. The actual internal representation is slightly different. The printer itself may introduce some roundoff. This is dependent on the underlying lisp implementation.
The same happens for 1e-6.
Based on the printed result, I'm guessing you're using gcl. cmucl will print 1.38e-23 and 1.0e-6 in both cases. If you are using gcl, file a bug with the gcl maintainer to improve the printer.
Not a bug, therefore closing this report.