Hi again, Thanks to everyone who has returned comments on the pqs library. My current instinct is not to put it forward as a boost proposal at this time. Having worked on the library for some time I have found it an interesting project., however the recurrent theme from the feedback is that the documentation needs to be much clearer. I also think I need to demonstrate application areas. IOW are physical quantities a practical proposition? Compile time dimensional analysis is a great example for showing of C++ at its best. However I do often ask myself the question as to whether this is 'showing off ' for academic interest rather than practicality. IOW once one starts to use a physical-quantity type, one soon finds that it becomes impossible to 'mesh' the type with other libraries. Examples here are std::complex and matrices. In both cases it requires a reimplementation to account for the different return types. Another issue is that the physical quantity type is restricted to compile-time. A runtime type is certainly possible though it would be considerably larger as it would need to carry the dimension and unit information along with it at run time. IOW a collection of types representing physical-quantities does not seem to be complete without being based in a much larger framework, with a lot more utilities. Perhaps this is an example of taking strong type checking too far, and may be the reason that a physical quantities library will not become a practical proposition. Whatever.. the library is certainly a facinating curiosity at least, and my curiosity as to where it will lead is not diminished. Here for example are a couple of types representing homogeneous vectors and transformation matrices for 2D transforms. Note that operations such as concatenation, determinant, cofactor and inverse all work satisfactorily within the strong type checking: PQ == the physical-quantity parameter type ( eg length::m) K/PQ == the 'reciprocal' of the type ( eg reciprocal_length::div_m } N == numeric type ( eg double) rc_matrix<PQ>( // 2D transformation matrix laid out in row/column format //using a tuple of tuples N, N, K/PQ, N, N, K/PQ, PQ, PQ, N ); row_vector<PQ>( // 2D vertex in homogeneous coordinates implicit //conversion to/from x,y vertex<PQ>. N, N, K/PQ ); regards Andy Little