Agree. Usually, by convention in the US anyway, a percentage without definition or clarification is 'of reading'. So, 1% of reading, plus 100,000 inches is my kind of specification.
Hershal is right. That should be 10e-5. Otherwise, we need more context to understand.
If the reading is 0.01, then 0.01x.01=0.0001 + 10e-5 = 0.0001+0.00001=0.00011. This is what it is, but
this is what it means:
The uncertainty value for the reading specification changes proportionally with the reading, but the 10e-5 will always be 10e-5. The uncertainty will never be less than that, even if the reading was zero.