ISO film speeds are just recommendations--actual film speeds may vary due to meter sensitivity, lens flare, type of developer, agitation techniques, and a host of other minor factors. The person who posted the speed of 250 for T-Max 400 was simply giving you the speed that he/she had found worked best for them. My speed for T-Max developed in Rodinal is 250, but I use 400 for PMK. See my charts at http://unblinkingeye.com. I think you can probably get a full 400 if you use T-Max developer at the recommended times on the bottle--my problem with T-Max developer is its expense.(posted 9167 days ago)