Does the example dataset you provided have wrong values matched?
Create column dry weight g/l and rename Time h to time h in reflectance data:
Concatenate the dry weight data to that:
Select reactor and Time h column and Sort by them.
Select missing value in dry weight -> select matching cells -> invert selection
Now you can jump around the table to find closest values:
At this point you could create some helping formulas or scripts to calculate the nearest value for example something like this to further reduce the data:
Names Default To Here(1);
dt = Current Data Table();
r = dt << Get Selected Rows; //selecting of wanted rows could be done in script instead of datatable
r_min = r - 1;
r_max = r + 1;
dt << Subset(rows(Sort List(r||r_min||r_max)), Selected Columns(0));
At this point you could most likely copy-paste the dry weight time values to new column and create formula to calculate closest row.
This is what join nearest rows would return when Join is used:
With Update it wont create as many messy columns:
UI of the tools seems to have some problem on table selection... and user has to make sure correct tables or selected or the tool will do self-join.
-Jarmo