▁thick ness . ▁With ▁a ▁typical ▁value ▁for ▁spher ical ▁aber r ation , ▁the ▁minimum ▁pro be ▁size ▁is ▁usually ▁around ▁ 5 0   nm . ▁However , ▁with ▁Cs ▁corrected ▁micro scop es , ▁the ▁pro be ▁can ▁be ▁made ▁much ▁smaller . ▁ ▁Pract ical ▁consider ations ▁▁ ▁Pre cess ion ▁electron ▁diff raction ▁is ▁typically ▁conducted ▁using ▁acceler ating ▁volt ages ▁between ▁ 1 0 0 - 4 0 0 ▁k V . ▁Pattern s ▁can ▁be ▁formed ▁under ▁parallel ▁or ▁conver gent ▁beam ▁conditions . ▁Most ▁modern ▁T EM s ▁can ▁achieve ▁a ▁t ilt ▁angle , ▁ φ , ▁r anging ▁from ▁ 0 - 3 ° . ▁Pre cess ion ▁frequencies ▁can ▁be ▁varied ▁from ▁H z ▁to ▁k Hz , ▁but ▁in ▁standard ▁cases ▁ 6 0   Hz ▁has ▁been ▁used . ▁In ▁choosing ▁a ▁pre cess ion ▁rate , ▁it ▁is ▁important ▁to ▁ensure ▁that ▁many ▁revolution s ▁of ▁the ▁beam ▁occur ▁over ▁the ▁relevant ▁expos ure ▁time ▁used ▁to ▁record ▁the ▁diff raction ▁pattern . ▁This ▁ens ures ▁ade qu ate ▁aver aging ▁over ▁the ▁exc itation ▁error ▁of ▁each ▁reflection . ▁Be am ▁sensitive ▁samples ▁may ▁dict ate ▁shorter ▁expos ure ▁times ▁and ▁thus , ▁motiv ate ▁the ▁use ▁of ▁higher ▁pre cess ion ▁frequencies . ▁ ▁One ▁of ▁the ▁most ▁significant ▁parameters ▁affect ing ▁the ▁diff raction ▁pattern ▁obtained ▁is ▁the ▁pre cess ion ▁angle , ▁ φ . ▁In ▁general , ▁larger ▁pre cess ion ▁angles ▁result ▁in