|Our phosphorescent ruler is made of rugged PVC foil onto which a millimetre guide and the spacing of many combs which are in use for SDS-electrophoresis are printed with a phosphorescent ink.
Just shortly expose to light and position your blot on it during exposition of the film. You don't have to make unsightly marks on the blot.
The ruler is compatible with aqueous solutions. When using it with Coomassie stained gels (especially the not well destained ones), the gel should not come into direct contact with the ruler - just cover it with a plastic foil.