Chair & Pin As per IS code.

Can anyone explain the chair details as per IS code which we had provided in slab to maintain proper spacing for both mesh of reinforcement. with specification of his both leg max length if any mentioned in IS code.
 
Can anyone explain the chair details as per IS code which we had provided in slab to maintain proper spacing for both mesh of reinforcement. with specification of his both leg max length if any mentioned in IS code.
as per IS 456:2000, chair shall be fixed 1 no in 1 Sq.M. however we need to understand the requirement of chair. it's a tool to maintain the spacing between two separate layers of slabs, footing etc. normally lower dia rebar tends to more sagging while placing in top layer. So may be in this case, chair may be required more than recommended in standard and while it is for higher dia, it may be less that recommended by standard. So it's all depends upon the site engineer, chair shall be provided as per requirement to avoid sagging in top layer. there are no such standard for legs. It may be provided with 2 x spacing of bottom rebar.