1. We illustrate some of the other choices as variations compared to our central value: α S (Mz) = 0.1156 → 0.1196 New H1 ‘optimized’ parametrization New ZEUS-JETS ‘optimized parametrization Old ‘in-between’ parametrization with ‘humpy’ gluon solution

2. Comparison of central fit plus total uncertainties to variations with α s (Mz)=0.1156 OLD/NEW are the same apart from high-x for the sea. STOP PRESS: the new NEW with fc=0.15 non-dynamic but Q20 and mc variation of fc, looks EXACTLy like OLD Preliminary status requested HERA I PDFs OLDNEW

3. Comparison of central fit plus total uncertainties to variations with α s (Mz)=0.1196 OLD/NEW are the same apart from high-x for the sea STOP PRESS: the new NEW with fc=0.15 non-dynamic but Q20 and mc variation of fc, looks EXACTLy like OLD NEWOLD

4. Comparison of central fit plus total uncertainties to parametrization variation using: New H1 optimised parametrization Old/new are the same Preliminary status requested HERA I PDFs NEWOLD

5. Comparison of central fit plus total uncertainties to parametrization variation using: New H1 optimised parametrization OLD/NEW very slightly different at high-x Dbar STOP PRESS: the new NEW with fc=0.15 non-dynamic but Q20 and mc variation of fc, looks EXACTLy like OLD NEWOLD

6. Comparison of central fit plus total uncertainties to parametrization variation using: New ZEUS-JETS optimised parametrization OLD/NEW look the same Preliminary status requested HERA I PDFs NEWOLD

7. NEWOLD Comparison of central fit plus total uncertainties to parametrization variation using: New ZEUS-JETS optimised parametrization OLD/NEW look the same apart from very high-x Dbar STOP PRESS: the new NEW with fc=0.15 non-dynamic but Q20 and mc variation of fc, looks EXACTLy like OLD

8. Comparison of central fit plus total uncertainties to parametrization variation using: the ‘humpy’solution for the h1/zeus parametrization. At Q 2 =4 (right)GeV 2 where the humpy structure is more visible OLD/NEW look the same Preliminary status requested NEWOLD