These notebooks contain Harold Holcroft's notes from trials of locomotives, whilst working on the rebuilt E1 and D1 locomotives, as well as developing N class locomotives. The books feature various readings taken along the way, and limited notes. Most have an index on the cover featuring date, train number and route taken. Locomotives featured include C-Class 270 and 298; D-Class 574; D1-Class 487, 489 and 735; E-Class 515; E1-Class 19, 67, 160, 163, 165, 179, 497, 504, 506, 507 and 511; H-Class 329; L-Class 761, 766, 770, 772, 773, 776, 778; K-Class 790 N-Class 810-823.